I think JimL can provide an answer to that question ........ are you there Jim? Funnily enough we were just discussing that point but I won't steal his thunder.
As simple as adequate visual cueing. Whilst this may not be an issue with ground level helipads, it surely is for elevated.
Take for example a helicopter which has a dynamic vertical procedure with plenty of power in reserve; if the engine failure is recognised at just before TDP of say 30ft, the aircraft will continue to accelerate upwards (some to higher than 60ft).
If the elevated helipad were only 1D, sight of the landing surface would in all likelihood be lost and the reject would be problematical (not for those test pilots who do this every day but for the average pilot).
For this reason, AC 29-2C has a provision that:
Quote:
Conduct of the Test. Vertical takeoff profiles should be flown from a pad simulating operational conditions because the sight picture may be critical to successful OEI operations, particularly for elevated heliports. At all points on the vertical takeoff flight path up to the TDP, the pilot, with reasonable head movement, shall be able to keep sufficient portions of two heliport boundaries (front and one side) or equivalent markings in view to achieve a safe landing in case of engine failure...
This is exactly the problem for those pilots who fly from rooftop helipads or from wellhead platforms where there are no obstructions topside.
One of the issues is that test flying for helipad procedures is sometimes conducted from a square painted on the runway; this provides no problem for hitting the target on rejects as there is sufficient peripheral visual cueing.
A further issue is the designation of elevated helipad; in JARs (not sure about other regulations) this is when the operating surface is 3m above the surrounding surface (triggering the higher requirement). This has been recognised in JARs and there is a facility to apply for a derogation (to the lower limit) based on an assessment of the pad and the visual cues.
The issue is more serious with larger helicopters with less than optimum Fields of View (FOV); with smaller helicopters the pilot tends to sit close to the door - where the visual cues can be maintained for longer. The best vertical procedure I have seen is the one which is provided for the Bell 427/429 where the pad can still be seen at a height of 120ft with the disc at the back and side of the pad (a very steep vertical/oblique). This profile could obtain a 1D CAT A approval.
Its hard to say whether the tail drive failed from overheating or lack of lubrication, most probably it was a bit of both. What I was alluding to was the fact that its dealing with the overheating that is the primary issue, dealing with lubrication is secondary and this is why the aircraft I fly has a system whereby synthetic glycol is sprayed onto the hot parts. The tank holds sufficient to last 50-odd minutes, though its only certified to run for 30 minutes following complete loss of oil. As far as I am aware, the glycol does not really lubricate well, it just transfers the heat away. If you used grease, it would get very hot very quickly to the point that it might vapourise and I am not sure it would do much of a lubrication job. It would certainly make a lot of smoke!
Thanks Jim. Great info, but I'm still confused about the 1D v. 1.5D bit. While the guidance material talks about sight picture/visual cueing, I would think that 0.5D would make very little difference from a high TDP (say >75').
Great point about the larger Part 29 aircraft and their field of view. Do the ops rules have a say? Seems like operators would need to have some 'ground rules' for how large an aircraft they can use at a given facility...
Hullaballoo, it is the 'ops rules' that specify the 1.5D. You will find them in ICAO Annex 6, Annex 14 and the ICAO Heliport manual. Obviously not all regulators follw these guidelines, so they may not apply to all operators.
HC am I correct in recalling you had a 330J with oil cooling failure a long while back? I believe the lubrication capacity of the oil deteriorated very rapidly.
In fact the ICAO Annexes (6 and 14) defer to the Flight Manual, specifying only in the absence of limits.
My remarks were directed towards the issue of adequate visual reference using '1D' only as a general example. Flight Manuals tend to provide their limitation in specific units of measurement - not in proportions of 'D'.
The limits in the FM are a result of a CAT A certification exercise and so are directly applicable to each procedure (hence the two limits: one for ground level helipads; and the other for elevated helipads).
In the example you use, there would have to be a practical demonstration of appropriate cues on the surface - hence, each helicopter is assessed in its own FOV environment.
In fact the AC 29-2C guidance is not comprehensive enough because it is not the cues at the TDP that are the main issue it is those at the height/position where the aircraft stops its ascent following an engine failure at, or before, the TDP.
JARs are sophisticated in their treatment of size of helipads in PC1; providing it can be shown that there is no probability of a rejected take-off (i.e. the case where a continued take-off is always possible), the CAT A helipad size limits do not apply. This is of most use for HEMS aircraft which are operating to hospitals with historically smaller helipads (smaller than those required for CAT A).
Large Helo Autorotation/Certification vs Operational
Crab, I believe that you have it right, and allow me to expand just a tad on the technique used in the S-92 video.
FAR 29.79 and 83 provide the requirements and AC 29.2c, pages B-83-84 provide general guidance. One will note the absence of a required minimum landing speed, and the AC only recommends a speed under 40 kts.
Another reality surrounding the question of what is the best way for the manufacturer test pilot to proceed is that the machine in question is typically the envelope expansion/structural test aircraft, and thus has the maximum instrumentation installation. That makes it a very dear commodity, with serious consequences should it be seriously damaged.
It is clear in reading the advisory circular that the FAA intent is clear and stated in AC 29.75A.b.(2)(vii).(C): " The intent of this rule is to demonstrate controlled touchdown conditions and freedom from loss of control or apparent hazard to occupants when landing with all engines failed."
There is no instruction or direction that requires the demonstration to perform multiple power off landings to replicate what might be the best operational power off landing procedure for conditions such as: landing in forest, landing in a soft, or muddy plowed field, or the ocean. Certainly, ( and I think you were referring to these conditions ) in any large single rotor machine, these conditions would make the pilots approach to ensuring tail rotor clearance during the end of the flair a bit different, as the pilot will want to minimize the touchdown groundspeed.
As to the question of practice and build-up, its not very complicated. Since the pilot knows that at sometime in the future the landing has to be made, he will do a powere recovery auto at the end of other test flights, to look at the flare entry speeds and the flare angle required to temporarily zero out the rate of descent. Then, when its time to do it for real, two or three power recoveries and then finish it.
This is the approach used by the pilots who did the CH-53A, the S-64 E and F, and that I used in the S-67, UH-60, SH-60, S-76 and S-92. No dents or dings in any of them. I am sure that other OEM test Pilots can attest to approaching this first-time task in a quite similar way.
Sultan, you may not recall, but early in the SH-60B program, there was a tail drive problem that occurred on an SH-60B stationed at Mayport, Fl. Crew made an uneventful auto to the water and all swam away. The ship floated for quite awhile and a picture was taken of the tail of the aircraft sticking out of the water with a perfectly preserved, totally undamaged tail rotor.
This was a typical USN flight crew.
The ship was recovered and as I recall, there was a maintenance issue with the TR driveshaft coupling that of course is broken every time the tail is folded.
Sultan - I'm guessing from your profile that you haven't actually flown any EOLs. How does that mean you know what you are talking about?
As John points out, TPs have to use an incremental approach to completing an EOL on an aircraft so you work up to it gradually rather than just hacking the engines and giving it a go - the aim is not to trash the very expensive aircraft whilst still proving it can complete an EOL with crew survivability.
Zero speed touchdown EOLs are easy peasy in a small, light helo, especially with a bit of wind to help but you will crunch a big helicopter trying to reproduce the same thing - that is why they go for a fast touchdown speed, letting the (generally large) undercarriage absorb some of the energy.
Folding tails are notorious for causing TR problems - the disconnect coupling needs to be rigorously serviced and positively engaged and checked before flight.
At least the 92 can "autorotate" to a landing....something your favorite bird cannot do at all. Your favorite machine cannot survive dual engine failure....or loss of the last engine when in the helicopter mode below 1600 feet AGL.....or AVRS below that same approximate altitude. Bell admits to those problems.
Perhaps you might spend some time worrying about that rather than wasting our time suggesting the Sikorsky Products cannot survive a tail rotor failure which you do without any corroborating source material.
Aha.. a cross-thread challenge.
Now, how would an EH101 fair? Would it crash attempting an AR with dual engine failure or does all three donks have to be killed for it to mess up and break into pieces whilst flaring..?
My favorite helicopters are the Bell 47, 206's, 214B and the 412. All autorotate to touchdown so easily that they are not just demonstrated once, but practiced all the time. After a while it was actually kind of boring to sit through all the ones I participated in, except for the 214B which allowed you to do a point touchdown, lift off and move 20 feet or so to the final spot only using the rotor inertia. That was a hell of machine.
My favorite helicopters are the Bell 47, 206's, 214B and the 412. All autorotate to touchdown so easily that they are not just demonstrated once, but practiced all the time.
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