It may be slower than its competitors, but the power of Bell's 427 light twin turbine, simplicity of operation and overall comfort impressed Flight International's test pilot Peter Gray/MIRABEL Beginning with a clean sheet of paper, a list of desired design criteria and a rigid purchase price goal, Bell Helicopter Textron believes that, in its Model 427, it has produced the 'right sized' light twin-turbine helicopter for corporate users, offshore operators and emergency medical services. The company decided there was a niche for a 2,720kg (6,000lb) gross-weight, twin-engined helicopter with fewer parts, reduced maintenance, low vibration, smooth ride, quiet operation and exceptional Category A performance. Bell says it is pleased with the market reaction, with more than 80 orders placed so far. Competitors are the Agusta A109, Eurocopter AS355 and EC135 and MD Helicopters MD902 Explorer.

• Flight Training Manual

Bell 407 Tailboom/Fuselage Former Ring Fixture P/N 407TBF $900.00 $175.00 (Rental) Used for replacing tailboom/fuselage former ring or tail boom attach fittings on the Bell 407 only. The top two holes are larger than the 206. This fixture comes with 2 drill bushings. One for the top holes and one for the bottom holes.

Canadian certification of the 427 is expected this month, to be followed by US and European approval. Initial certification will be for visual flight rules (VFR) operation, but Bell plans for dual- and single-pilot instrument flight rules operation, and Category A approval for runway and helipad operations. Bell also plans to increase the maximum gross weight to 2,950kg, for which the Pratt & Whitney Canada PW207D engines have the required capability. The switch to the D-model during development has already increased the helicopter's payload.

The PW206D has a 30s one engine inoperative (OEI) rating of 610kW (820shp), although the transmission will allow only 485kW. But this means the pilot is guaranteed 485kW throughout virtually the entire flight envelope, up to high altitudes and temperatures. This should be more than enough to allow recovery from a sudden loss of power in most situations. The next steps down are the 2min OEI power rating of 580kW, a 30min OEI of 560kW and a continuous rating of 530kW. Combined twin-engined 5min take-off power is 1,060kW, with a transmission limit of 650kW for all twin-engined operations. Maximum continuous power is 930kW. Bell has held the VFR 427's purchase price to $2.2 million and direct operating costs to under $440/h.

This has been achieved by using 33% fewer cabin parts than in the single-turbine 407 and 40% fewer transmission gears than in the twin-turbine 430. Simplified assembly Flight International was invited to Bell's Mirabel, Canada, commercial helicopter plant to evaluate the 427, affording an opportunity to see the aircraft in assembly. The fuselage is built in five main structural sections. The hybrid composite/metal side panels are of one piece, with a hinged or optional sliding door that is a precise fit and interchangeable between aircraft. Similarly, the roof is of one piece, with all components attached to the top, making maintenance easier and quicker and providing added headroom. The forward fuselage is supported by two long alloy keel beams that allow plenty of room for the battery, avionics and other equipment. The tail boom and stabiliser assembly is again of one piece, for added strength, and is constructed with heat resistant materials.

The helicopter has a smooth, low drag exterior, that is easy to paint and to maintain. There is no external gutter on the doors (it is incorporated into the internal seal), reducing drag and noise.

The windows are a precise fit, with screws replacing rivets. The windshield is bulged to increase rigidity, so no wipers are required. A bubble window for the pilot will be available for vertical reference long-line operations.

The composite cowlings are large, to improve access, and do not require a screwdriver or other tool to open. The baggage compartment is on the right hand side, where the pilot can see what is going on. It is small compared with competing helicopters, however - 0.87m³ (30ft3), compared with 1.2m³ for the EC135. But there is additional baggage space in the cabin, on a parcel shelf and beneath the seats. The 11.3m (37ft)-diameter main rotor uses the proven 'soft-in-plane' hub design of the Model 407 and military OH-58D, with its failsafe multiple load paths. Elastomeric bearings and dampers allow fewer moving parts and less lubrication.

A top cover not only helps reduce drag, but protects components such as dampers and thrust bearings against sunlight. The rotor blades are composite, with nickel-plated leading edges for erosion resistance. Rugged gearbox Under the hub sits Bell's new 'flat-pack' gearbox. This has fewer moving parts than previous transmissions.

It is of rugged design and has run for 4h 32min under high power without oil - quite an achievement. Time between overhauls is set at 3,000h initially. The engines drive directly into the transmission, eliminating the need for a combining gearbox. A driveshaft goes straight to the tail rotor gearbox, dispensing with the inter-mediate stage.

This also has a comforting run-dry capability. The main gearbox is designed to remove the 'bounce' that some other Bell helicopters suffer from when the rotor is running on the ground. Indeed, the whole assembly sits on Bell's Liquid Inertia Vibration Eliminator (LIVE) pylon suspension system, which eliminates the natural 4/rev vibration pattern of the main rotor. A single hydraulic system is standard, and dual hydraulics optional. The crashworthy fuel system is simple, using the engines' own pumps to suck up the fuel. The only other pumps are to transfer fuel from aft to forward tanks. If the fuel starts to get out of balance, the pilot is warned.

Bell has separated the fuel system from hot engine parts by putting all the components in a closed vapour box, eliminating heavy firewalls. In emergency medical services (EMS) configuration, one of the 130 litres (34USgal) forward tanks has to be reduced in size to make room for the stretcher. This lowers endurance by about 20min - not a big penalty. Alternatively, a stretcher can be installed diagonally without removing the tank. The interior comes in various configurations. The standard eight-place utility version has two rows of three seats facing each other and two in front for the pilot, plus one passenger.

There is an optional all-forward-facing eight-seat configuration. Then there are the usual VIP interiors, with fewer seats, and consoles for refreshment and entertainment centres.

The 427 has crashworthy seats and shoulder harnesses all round. Empty weight is 1,705kg. Our test aircraft, with all the extras on board (avionics, particle separator, rotor brake, dual flight instruments and controls and other items), totalled 1,810kg. At this weight, with an 82kg pilot and a full fuel load of 628kg giving a range of nearly 740km (400nm), payload available is 200kg, according to my calculations. This will be increased by 225kg if the maximum weight is increased to 2,950kg as planned.

Alternatively, you can fill the seats and see how far the allowable fuel load will take you. Our empty weight, plus eight people at 82kg each, added up to 2,465kg, leaving 255kg for fuel - enough for 1.16h with no reserves. For underslung load operations, for which maximum weight is increased to 2,950kg, the pilot plus 1h fuel gives a 923kg payload. The aircraft can hover outside ground effect at 2,950kg, using 5min take-off power up to 5,000ft (1,500m) on a standard day. At maximum continuous power, which is more desirable as it leaves plenty in hand, I estimate the aircraft can hover at 2,950kg up to about 4,000ft.

This is good news for potential underslung load operators. The load hook is designed to lift 1,360kg, so there is plenty of margin. The flight manual limits climb rate to 2,000ft/min (10.2m/s). The aircraft could exceed this, but would require a movable elevator for longitudinal stability - 2,000ft/min is enough for me. The manual's height-velocity (HV) diagram shows those combinations of low speed and height where a single engined landing cannot be guaranteed to be trouble free.

This 'avoid' area could have been smaller, but the first reliable airspeed indication is at 20kt (37km/h), so Bell extended the HV area to that airspeed. In fact, the avoid area does not come into effect at any weight below 2,720kg or any height below 7,000ft density altitude, proving the 427's excellent power to weight ratio. Climb rates The single engined rates of climb, even at 2,720kg, far exceed Category A performance requirements and only start to drop below 200ft/min at 8,500ft when using the 30min power rating, or at 6,500ft when using maximum continuous power.

Bell senior test pilot Eric Emblin walked me out to the aircraft. The day was fine with an ambient temperature of 9°C, which reduced our pressure altitude of 500ft to zero.

The wind was 5-12kt and our start-up weight was 2,740kg. Emblin took me round a typical preflight inspection. Access to the important areas was easy. One nice touch, especially in bright sunlight, is that sight glasses go white if the fluid level is low.

The vertical stabiliser is offset 9°, which helps offload the tail rotor. On low skid gear, the main rotor blade tips are 1.93m above ground level, increasing to 2.17m on the optional high gear. We had three passengers to help get our weight up to maximum. Our 1.88m-tall passenger was comfortable in all the seats, with adequate legroom and good outside visibility. The seats are energy attenuating, collapsing downwards in a crash or heavy landing.

Bell has not yet decided where to put any life rafts. I installed myself in the captain's right hand seat. The seat is fixed, but, by adjusting the pedals, I was able to find a comfortable position with hands and feet resting easily on the controls, in sight of and in touch with everything else.

I was impressed by the simplicity of layout, although our aircraft was configured for single-pilot VFR. This is mostly because of the integrated instrument display system (IIDS) which incorporates on two small liquid-crystal displays information that used to be spread out over the instrument panel. The IIDS shows clearly engine and rotor parameters, temperatures, pressures, ammeter, voltmeter, fuel quantity and temperature, clock, hourmeter, outside air temperature, maintenance functions, power assurance checks, exceedance monitoring, warning and recording and the advisory/caution/warning panel. Power assurance, maintenance and exceedance information can be downloaded. Some exceedance information is recorded permanently and can only be removed by the engine manufacturer. The IIDS sits conveniently in the middle of the panel, to allow both front seat occupants equal access. In front of me was a comprehensive blind-flying instrument panel, above which are the OEI training switch, fire extinguisher buttons, master caution light, full authority digital engine control (FADEC) panel and low rotor RPM warning lights.

Caged fuel valves are located at the bottom of the panel, while large blank sections on the right and left sides of the panel provide room for extras. The small centre console is taken up with a comprehensive set of communication and navigation equipment. There are 42 advisory/caution/warning messages, any one of which will sound a gong to attract the pilot's attention to the IIDS. Rotor RPM falling below 95% and FADEC failure have their own audio warnings. I liked the combined digital and analogue display of gas temperatures, torques and the triple power- turbine/rotor RPM tachometer. Maximum continuous power and RPM indications are in green.

At the 12 o'clock position, they turn yellow when take-off power is used and red if it is exceeded. The triple tacho does all this at the 9 o'clock position. In single engined operations, all these instruments automatically revert to single engined configuration and limits. Although the flight manual has the actual figures for all these limits, the pilot can instead rely on the colour displays and other indications.

Buttons below each IIDS screen bring up displays of whatever system the pilot requires and, in the event of a malfunction, will show what has happened and where. The cyclic pitch stick and collective pitch lever, the latter with two in-line throttles on the end, came nicely to hand, each having their own friction that I adjusted to my liking. I noted that there was no guard on the hook release switch on the cyclic. Conscientious external load operators will have to fit their own. The overhead panel has the usual generator and light switches, rotor brake and circuit breakers.

The latter are grouped logically and the switches all go forward or down towards the instrument panel to select on/normal. The cockpit has a bright colour scheme and exudes an impression of space and light. All round visibility is excellent. Start-up procedures As the electrical power came on, the FADEC and fuel transfer control units self-tested and indicated all was well.

One test button brought on all the lights. Emblin ran round the cockpit, setting it up for the start, including interrogating the IIDS for any previous exceedances. I selected start on the first engine. All I had to do then was monitor the gas temperature display, hand on throttle, and ensure the needle did not overtake the small triangle, in which case the throttle is closed.

The start was cool and slow. The other engine was started next, the throttles wound open and placed in the flight lock and, after checking there were no messages on the IIDS, we were ready to go. In a hurry, engines can be started in the 'flight' position. We were now at the maximum weight of 2,720kg. I pulled up into my first hover,which was easily controlled and steady. I relaxed and allowed the aircraft to do the work. A glance at the IIDS showed that we were using well below maximum continuous power and the excellent presentations showed how much power I had in hand.

We had enough available to hover on a single engine. There are no wind sectors that affect the handling of the 427. I turned through 90°, landed, and continued thus all the way round. The aircraft behaved impeccably when out of wind.

The fuselage remained level, and noise levels were benign, even without my headset. The aircraft is cleared for 35kt sideways and backwards flight - we went to 38kt backwards with no ill effects. The aircraft behaved impeccably and I still had pedal in hand to overcome any yawing while hurtling sideways. There are no limits to turns on the spot, so I handed over to Emblin to do his worst. We went round very quickly, using about 90% of the 100% continuous torque available. We moved to forward flight, keeping an eye on the rate of climb so as not to exceed the 2,000ft/min maximum. While still heavy, I carried out a single engined landing, coming to the hover first.

The engines went to the 2min power level and briefly into 30s power. There was no rotor droop.

This was impressive, even at our density altitude of zero feet. The instruments, with their colour changes and power level warnings, were helpful. There is a switch on the lever which allows the pilot to pull even more power, if required to save the aircraft, but damage to the engine and transmission will result.

The advisory panel indicates '30SEC', '2MIN', or '30MIN' whenever the pilot is using more than maximum continuous power While still heavy, we went back up, settled down straight and level, and reverted to single engined flight, with the remaining engine at maximum continuous power. We easily achieved the single engine Vne of 100kt. Emblin then restored the second engine and I held maximum continuous power straight and level.

We achieved 138kt indicated airspeed, which equated to 136kt true airspeed. This is a little slow, however, compared with similar twins which I have tested (148kt for the A109 and 145kt for the EC135). The Vne is 140kt up to 6,000ft and was easy to achieve in a slight dive.

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Thanks to the LIVE anti-vibration system, the flight had been exceptionally smooth and there was no noticeable increase at Vne. Turns in both directions at Vne were carried out and again the ride was smooth.

Although the aircraft has been designed to withstand +2.5/-0.5g, US Federal Aviation Regulation Part 27 certification does not allow aerobatic manoeuvres, so the flight manual limit is +2g with no negative g allowed. We pulled 2g in 60° banked turns in both directions. Handling remained benign. While at maximum continuous power on two engines, I asked Emblin to simulate an engine failure. Rotor RPM dropped and stabilised at 94% before I lowered the lever to restore rotor speed. This acceptable result means that, even if the pilot does nothing, the aircraft will continue to fly safely. Next, we tried settling with power/vortex ring, a condition in which the aircraft will sink at low forward speed, with power applied, because vortices that cause loss of lift, turbulence or even rotor stall and loss of control develop around the main rotor.

We tried to induce the condition and eventually got a rate of descent build-up to 1,500ft/min at zero airspeed, but there was still good cyclic control for recovery. I asked Emblin to go from low power to 100% torque and back as quickly as he dare, so that I could evaluate the engine governing systems. We got just a 1% power turbine and rotor RPM change - very impressive. Emblin switched off one of the generators, the gong bringing our attention to the caution panel. He brought up the electrical system page on the bottom IIDS screen, showing exactly what had happened.

The remaining generator was able to supply all the power required without reaching its maximum output. I do not like the engine fire drill, which requires the pilot first to close the throttle on the offending engine, shutting it down, then press the fire extinguisher button, which also shuts off the fuel. If the pilot closes the wrong throttle, he will have a double engine failure. I recommend first pressing the extinguisher button, which does everything required to put out the fire, then closing the throttle while watching rotor RPM to make sure it is the correct engine. As we returned to base, Emblin switched off the single hydraulic system. Again, the warnings were obvious and the IIDS hydraulics page showed us what had happened. With forward speed, the aircraft is easy to control.

The test comes when trying to hover and land. Our aircraft did not have the spring or trim switch fitted to help with cyclic control. Although the flight manual recommends a 15kt running landing, I was able to come to a steady enough hover. A little practice, I feel, would give me enough confidence to land on an offshore platform. Training mode We next explored the single-engined training mode, a realistic simulation which allows a pilot to practise without using single engined power, which eats into cycles.

By selecting an engine on the panel at the top of my instrument panel, Emblin simulated a sudden failure. The top IIDS screen immediately switched to single engine presentation, with different scaling. I saw the 'good' engine go to high power and the rotor droop. In reality, the 'failed' engine reduced to about 150kW and the good engine, although showing maximum power, was using no more than maximum continuous. The lower IIDS screen showed what was happening. If the FADEC fails, the gong will sound and the IIDS will show what has happened. The FADEC will freeze the fuel flow at the point of failure and automatically revert to manual throttle.

All the pilot has to do is take the throttle out of the 'fly' position and use it to control the affected engine to just below the governed engine. To practise this, there are 'manual' switches on the FADEC panel, one of which Emblin selected. The gong sounded and the FADEC mode indicated 'MANUAL'.

I did an approach, go around, hover and landing, controlling one engine manually and taking care not to overspeed the rotor when lowering the lever fully for the landing. As a reminder to the pilot, Bell is to cross-hatch the needles of the affected engine displays. Emblin then simulated a tail rotor pitch control failure and did a good run-on landing at moderate speed. We found a slope and took the aircraft to its limits of 10° nose up, 5° nose down and 10° sideways. The aircraft was easy to handle, but I had to keep an eye open for the 'CYCLIC CTR' caution light, which informs the pilot that the stick is not central. We were unable to carry out autorotations because the aircraft was to have a different set of main rotor blades fitted to allow practice autorotations.

So we came in and shut down, interrogating the IIDS for any exceedances. From the pilot's viewpoint, the Bell 427 has sufficient engine power to operate safely and efficiently throughout its flight envelope. Similarly, there is sufficient main and tail rotor power to avoid running out of control. The aircraft offers simplicity of operation, particularly in single pilot IFR, and appears able to handle malfunctions without overwhelming the pilot. For the passenger, the helicopter offers comfort, sufficient space and acceptable levels of noise and vibration. The operator, looking for efficiency, reliability and cost effectiveness as well as safety, will no doubt be impressed by the 427's low maintenance requirements.

Nick Lappos et al The question I believe was more about what these subjects ARE rather than what one's opinion of their relevance is. Having recently been asked the same question by a customer I had to explain the reality of the situation rather than the academics of what it ought to be. I have to say that what Nick says makes a lot of sense but as we all know our performance mantras have their origins in the fixed wing world and it is likely to be a while yet before we some common sense creeping into the world of helicopter performance. What the standards posed by Cat A (Group A if you are a Brit) and Class 1 have done is forced the manufacturers to produce helicopters that are almost able to fly throughout the flight range on one engine.

Irrespective of your thoughts about the applicability of 'Cat A' I reckon this is a 'good thing'. I recently saw a picture of Bo105 upside down in the 'oggin' in the GoM after it had suffered a single engine failure but been unable to maintain height at the weight he had elected (been forced to more like) operate. So - in the big debate about Cat A, is it a good thing or a bad thing - me, I plump for giving the guys a bit more to play with in an unforgiving and unpredictable world. Save the Cat B stuff for the military. Now I see that I haven't answered his question either and I'm not in the mood to write pages and pages about helicopter performance so I'll leave that to somebody else. Does this help?

Helicopters are certified in one of several groups. For example, JAR classifications are 1, 2 and 3, which are broadly equivalent to the UK Groups A, A(Restricted) and B (see the table below). These are different from Airworthiness Groups, which dictate how well the airframe stands up to a forced landing. In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes: PassengersJAR ClassUK AN(G)R Over 19 1A 9-19 2A (Restricted). Less than 93B. Category A means multi-engined helicopters with engine and system isolation as per JAR-27/29, and Flight Manual performance based on a critical engine failure concept providing adequate surface area and performance capability for continued safe flight if an engine fails. In other words, in addition to making sure you have power available (by restricting MAUW) it provides space for rejected takeoffs and landings, and obstacle clearance.

Category B means single- or multi-engined helicopters not fully meeting Category A. They are not guaranteed to stay airborne if an engine fails and an unscheduled landing is assumed, possibly with some damage. Category A helicopters may operate in Performance Class 1, 2 or 3, but Category B machines may only be operated under Class 3. JAR Class 1 (Group A) helicopters offer the highest protection for passengers and require no forced landing provisions if the critical power unit fails - the machine can either land within the takeoff distance or continue (safely) to a suitable landing area, depending on when the failure occurs (that is, before or after CDP - see below).

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Group A helicopters must (with one engine out) clear all obstacles vertically by 35 feet, and climb (after CDP) at 100 fpm to 500 feet, then continue at 50 fpm (1.5%) between 500-1000. They must be able to maintain MOCA in the cruise. However, there is an exposure time concept, measured in seconds, during which there is no guarantee of a flyaway or safe forced landing. The maximum permitted exposure time is a statistically derived figure, during which the probability of an engine failure can be discounted. The idea is to allow older helicopters to operate while new stuff comes in, and is due to expire (in JAA-land) in 2010.

JAR Class 2 machines, or Group A (Restricted), are slightly more flexible and can operate to a slightly less demanding regime, so you have a wider choice of landing sites. They have a limited exposure (although occupants and third parties must remain uninjured) - and can normally continue safely, except when the failure occurs early in the takeoff or late in the landing, so a forced landing may be required, under conditions that allow it, in terms of weather, light and terrain - those done from elevated pads in non-hostile conditions must be done by day only, otherwise you must abide by Class 1.

Otherwise, cloud and visibility must be above 500 feet AGL and 800 m. In other words, up to 500 feet above the site level, you have to be able to see and avoid obstacles. After that, when you are presumed to be IMC, you must meet Class 1 requirements up to 1000 feet above the site, so watch your takeoff weight (the rate of climb should be 50 ft/min net). JAR Class 3 multi-engined types (that is, Group B, for multis below 2730 kg) may have to make a forced landing, while single-engined types will (some multis share facilities and are not classed as real twins).

Public Transport operations must be done in sight of the surface, by day, with at least a 600' ceiling. Minimum visibility is 800m. Class 3 is not allowed in IMC or at night. An engine failure below 100 feet should ensure a safe engine-off landing, so no manoeuvring should be done. The JAR screen height is 35 feet, for takeoff and landing. There are no distance requirements.

I'm sure if I've got anything wrong someone will tell me! Paco, There are a number of points in your post which need clarification - you offered them up for comment and I will take up the challenge. Jim Thanks for the detailed explanation here. Firstly, when requesting a strictly Helipad Procedure departure profile from ATC, what is the correct request to ATC; I assume simply for a 'helipad departure', rather than Cat A /Group A/Class 1 departure? Secondly, to achieve Category A certification, with reference to rejects before TDP following a helipad procedure, what criteria for subsequent life/durability to engines and transmissions are specified/involved? Of course the acft must be operated within all the transient OEI limits in the FM, but when a manufacturer specifies a say 15 second power limit OEI, which is likely to be the limiting factor on a reject, what reduction if any to the TBO of engine/transmissions follow full use of that transient limit? On the face of it, this is a manufacturer question, but presumably the regulating authorities have specifications that prevent a manufacturer simply taking the view that the transient OEI limit is one that has a say 90% chance of the engine/transmission not failing in such use, though must inevitably then be immediately deemed unservicable and over-hauled?

Rotorspeed, Provided ATC know what to expect - the call is immaterial. The Flight Manual always contains the conditions under which engine limits may be used.

The only short term OEI limits that I am aware of are the 30 second plus the 2 minute limit - or for those which do not have a 30 second limit, the 2.5 minute limit (note that the AB139 does not use a 30 second limit - presumably because it is not required). A rejected take-off is unlikely to come anywhere near that time - unlike the continued take-off where the limits have to be observed and not exceeded. One of the problems seen in the recent past is the reluctance to pull up to limits by drooping the rotors on a reject - with the consequence of an increasing rate of descent and a hard landing. Fortunately most of the occurrences were in training and not during operations.

Depending on the engine, the use of the 30 second limit might result in maintenance procedures (I think that 212man has had something to say about that in the past with the EC155) but is unlikely to have a severe affect on the gearbox. Whatever the consequence it will have been pre-considered by the State of Design and the Type Certificate Holder and have been part of the certification process - and addressed in the Flight Manual or the Maintenance Procedures. Most of the profiles/procedures that I described in my last post and PC2e (offshore zero exposure departures), benefit from the use of FADEC (which protects the remaining engine and the transmission) and the stored energy provided by the additional NR. There have been discussions on FADEC limit override but I am not aware that this has led to changes to FADEC algorithms - that and blow-away power are really tools of last resort. The AS355N actually has a 15 second limit of 140% Tq OEI, (131% 2m 30 sec), so on a reject I assumed this would be the factor that determined max weight for Cat A ops. It would be useful to know how much of a bill might be incurred pulling that, so I'll check with maintenance! Somehow doubt the FADEC on this acft protects from exceeding the engine limits, resulting in Nr droop.

Are you saying that in some acft the FADEC will prevent exceedances in OEI conditions, even though the absence of that might protect the airframe and occupants, even if it trashes an engine? Assuming extreme circumstances, of course. Thanks jiml - that made a couple of points clearer, though there has always been some confusion in the use of the words group and category interchangeably for certification and performance purposes 'Paco, this contention is not correct (and if nothing else is taken from this post perhaps this will stick) helicopter are certificated in Category A or Category B; they are operated in Performance Classes 1, 2 or 3.' That's exactly what I said! 'In other words, the terms Category A and Category B (as opposed to Group A or B, or Class 1 or 2) are for certification purposes' So what do people mean when they say Cat A performance? A couple of points about the engine ratings etc.

Jim, I may be wrong but I would guess the reason the AB-139 does not have a 30 second rating is because it uses the PT-6. Generally the engines with 30 second ratings have new technology materials (such as single crystal blades etc) and I doubt that even the -67 version would have this. The point made about FADEC controlled engines limiting power at the expense of the airframe is a bit misleading I feel. For the type I am familiar with (EC-155 which has dual channel FADEC and no cockpit engine control other than a switch) when operting in twin engine operations (AEO) the FADECs will normally control the engines such that they remain within the normal AEO limits. However, that is not to say that they will respect the transmission limits and so it is still possible to 'overtorque' the MGB to prevent mishaps. If this proves to still be not enough power to prevent the problem, and continued application of collective results in the Nr drooping, the FADECs will abandon the AEO limits and apply the OEI 2 minute limits. If this still proves insufficient then tough!

The point I feel is misleading, though, is that this latter case is no different to a conventionally governed engine where if you pull in a big handful of collective, both engines will provide power up to the maximum contingency rating (2.5 minute) but no more. It's the same situation. The difference is that one limit is applied through the computer whereas the other is the topping setting set mechanically within the governing unit (AFCU).

Now, if you really want to see a system with an odd priority, look at the B-212 where the AFCU is designed to save the gearbox at the expense of the airframe. If you apply collective above 104.3% TQ the AFCU will prevent the engines producing more power. In fact it's worse than that; because the AFCU is respecting a torque limitation, if you droop the Nr (which you probably will do to prevent a heavy landing) the N2 will drop and so for a given torque value the actual SHP will be less. So the situation will escalate. Paco, I think that I have already covered your question in my first post:Category A also requires the provision of performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated; this data includes: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs.

From these procedures and graphs an operator/pilot can establish a complete OEI flight trajectory.and is the provision of procedures, masses and data in compliance with the respective rules of FAR/JAR 29.45 - 29.67 to the satisfaction of the Certificating Authority. This set of rules specify (along with the guidance in AC 29-2C): no descent below 15ft (when the TDP is above 15ft) in the take-off path; require a level surface over which the take-off is being conducted; no obstacles in the 'Takeoff path'; the provision of the minimum climb performance - i.e. 100ft/min up to 200ft at Vtoss and 150ft/min at 1000ft at Vy; and the provision of the respective distances. None of that is in question, the point that was being made was more fundamental - when, what and how? When is the operator required to apply the performance data, what obstacle clearance has to be shown and where is that specified? Clearly there is a difference of opinion as the highlighted section in the definition of Category A between the FAA and the JAA/ICAO indicates:(JAA) Category A, with respect to rotorcraft, means a multi-engined rotorcraft designed with engine and system isolation features specified in JAR–27 / JAR–29 and capable of operations using take-off and landing data scheduled under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight or safe rejected take-off in the event of engine failure.

(FAA) Category A, with respect to transport category rotorcraft, means multiengine rotorcraft designed with engine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landing operations under a critical engine failure concept which assures adequate designated surface area and adequate performance capability for continued safe flight in the event of engine failure.The JAA clearly believes that the provision of performance data must be supplemented by the appropriate operating rules in the JARs. The FAA does not as there are no helicopter performance rules in FAR 91 or 135 (unlike Appendix A to FAR 135 for 10 or more passenger airplanes). It is the operational regulation which must indicate how an operation can be conducted; certainly JAR-OPS contains not only the indication when to operate within a certain Performance Class but also provides the requirements, compliance with which will give appropriate obstacle clearance in PC1 (and PC2 - outside of the take-off and landing phases).

In the absence of performance rules in the operational FARs, the FAA have to rely upon an interpretation of FAR 29.1 and in particular FAR 29.1(c):(c) Rotorcraft with a maximum weight greater than 20,000 pounds and 10 or more passenger seats must be type certificated as Category A rotorcraft.The are a number of points raised by this approach: what rules apply to helicopters below that weight or with less passenger seats; and is the implication of this text that such helicopters must be operated only in PC1? The use of the language Category A rotorcraft might indicate that such helicopters will have to apply the Category A procedure - at least for every take-off and landing; I’m sure that was the intent when this text was amended on the 31st January 1983 (see the question posed by Mars on the last Category A thread that was answered by GLSNightPilot here (The problem that this latter point poses can be seen only too clearly when examining its implication to the S92 and the EC225. Clearly both of these helicopters are being positioned for use in offshore operations and if operations are reliant upon an interpretation of FAR 29.1(c), a Category A procedure will have to be provided and used when operating to helidecks.

All who followed the debate on the earlier thread will understand the implication of that. This is not a problem with JAR-OPS as operations in Performance Class 2 can be conducted when the number of passenger seats is 19 or below. For operations under FARs this has also been set aside for the time being with the issue of OpSpec H100 - which in other terms, specifies PC2 for offshore operations. 212man, Yes on re-reading my earlier post I gave the wrong impression - it is only the engines that are controlled. Jim PS Edited on 18th April for clarity.

One of the reasons why a manufacturer may choose not to use the 30 second ratings is that the transients allowed for this rating may not be as large as those allowed if you use the 2.5 minute ratings. (Go figure.) For certification purposes, transients are not allowed to be used to demonstrate performance, and even for category A machines, you cannot use the 30 second rating for the takeoff engine failure portion (strange as this may seem - read the Part 29 sections if you don't believe me). While this is a strange way to do things, it means that in a real engine failure you will have better performance than in the flight manual, which is a comforting thought. Thanks for all the input - in essence it appears there is a lot of debate surrounding why Cat A and Perf Class 1 and what term is used when.

Am I correct in saying: Cat A is a set of certification criteria Perf Class 1 implies you will have a successful departure/landing in the event of a critical power unit failure and indeed be able to stay aloft en route at the time of flight, BUT - It still appears that Cat A is often referred to as the profile and as such can be either a towering one (with reversal) for say rigs/helidecks or an acceleration to Vtoss for a departure from a field - which allows for a safe reject. SO in a nutshell - your aircraft is Cat A cetified but to be Perf Class 1 compliant you need to follow a particular profile on take-off or landing, which may require a reversal and then you need to ensure that you can stay aloft en-route. THe other great Q that was posed is that of Cat A implying OEI hover capability - Me thinks not?????? Now for the interesting part - how is the A109 Power/K2 a Category A 'equivalent' aircraft. Is this purely because the Part 29 def of Cat A is for large transport helicopters??

Canthover, Yes, Category A is a set of certificating criteria. Thanks for the info - all makes sense BUT - maybe I am being thick here: I had a look at the A109K2 RCFM (page 7 of App 25) says it is not certified to JAR 27 CAT A, but shows a whole whack of profiles for take-offs less than and greater than 2720 kilograms - so CAT A can be done as a back up or from a clear area with gauranteed safe reject. A quick peek at the CAT A back up (30 m recommended) appears to be for elevated helipads (helidecks). I presume then that there is no vertical climb profile that exists for the aircraft which is typical of the rig departure profile.

Take care, canthover, those profiles are not JAR Cat A if it is not certified that way. They are OEI profiles, and probably useful, but Cat A is a whole raft of requirements, not just a performance spec. For example, the required design virtues must be met, including isolation of engines and fuel, so that the probability of a dual engine failure is remote. A twin can have fantastic OEI performance and be woefully short of Cat A. This is not to say that the 109K2 is that way, just that it could be. Call the local tech rep and see what Agusta says about this. Canthover, Nick is confirming what was said earlier in the thread - frankly, I am surprised the the K2 is not certificated to Category A.

Once again please do not assume even a (genuine) elevated helipad procedure can be performed on a helideck - for the reasons stated earlier. As was said previously, to operate in PC1 or PC2 in Europe the aircraft must be certificated to Category A - the K2 might meet the equivalent safety permitted under JAR-OPS 3 but that would have to be established on a point-by-point basis (and be accepted by the Authority). Nick's point about the fantastic OEI performance could have been written about the Bell 427 and hence, as said earlier, the advent of the B 429 - which will be certificated to Appendix C of FAR/JAR 27. This thread may now be dead but I have a question about the CAT A data provided by the manufacturer that someone may be able to answer. In my type (S92) we have a graph for clear area MTOM/LM CAT A.

We also have graphs for OEI ROC as well as first and second segment OEI climb performance. My question is: Does the TOM gained from the the clear area graph guarantee a 150fpm at 1000'. From what I can see the MAUM from the OEI ROC and 2nd segment graphs doesn't tally with that gained from the clear area graph. Does the TOM gained from the the clear area graph guarantee a 150fpm at 1000'. From what I can see the MAUM from the OEI ROC and 2nd segment graphs doesn't tally with that gained from the clear area graph.

The S92 has variable Vtoss based Cat A MTOMs, with a maximum graphed value of 63 KIAS (although distance calculations go up to 70 KIAS). Below 63 KIAS Vtoss the aircraft is first sector limited and thus the RoC in the second sector (200-100') will be in excess of 150 fpm - assuming the MTOM is as per the WAT graph, and you are not using a Vtoss with a lower TOM. Above 63 KIAS Vtoss the aircraft is second sector limited and so the first sector RoC will be in excess of 100 fpm. Pressure alt at airfield: 0 ft, oat: 0'c, nil wind, ovc 003. Assuming icing conditions from 300ft on takeoff, max Vtoss. Basic WAT graph fig 4.9 using anti ice and RIPS gives MTOM 26200lbs Fwd climb performance graph 4.13 gives 25000 lbs for a 150 fpm climb OEI having applied the 440 fpm penalty. This agrees with fig 4.11 second segment graph.

This is a huge difference and led me to question what the basic WAT graph is guaranteeing as far as CAT A requirements are concerned. Some crews are relying completely on fig 4.9 even though it appears not to cover second segment requirements. I've just looked (albeit briefly) and, if anything, I think the penalty in Fig 4.13 should be greater than you state, as there is also an 85 ft/min penalty for Anti-Ice ON.

Going into the graph with 675 ft/min (to give 150 ft/min) then gives about 24,000 lb. Not having operated with RIPS a/c or in an icing environment (with this type) I haven't paid much attention to the subject. Some crews are relying completely on fig 4.9. Not sure I understand that - surely all crews are using the same planning methods (which hopefully doesn't involve using a printed graph)?