Inflight Breakup of a New Zealand Van’s RV-7
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Inflight Breakup of a New Zealand Van’s RV-7
The New Zealand CAA has released its final report on the 01 January, 2018 fatal crash of a Van's RV-7.
Here's a link to the report:
https://www.aviation.govt.nz/assets/...ew-Zealand.pdf
Regards,
Grog
Here's a link to the report:
https://www.aviation.govt.nz/assets/...ew-Zealand.pdf
Regards,
Grog
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That report is a good read! Off the top, I find it unlikely that the pilot was allowing the passenger to fly anywhere near those unusual attitudes. Sure, the passenger might fly some more or less straight and level, but not quasi aerobatics. I agree that this type of aircraft can build up speed very quickly when pointed down, particularly when carrying power down. I haven't flown the RV7, but I have flown the RV4, and they are very capable, and clean planes. They are easily capable of pleasing rolling, and getting too far over. A helicopter pilot would probably quite enjoy the solid feel of this plane in unusual attitudes, and let it get too far. Further, a helicopter pilot will be naturally adverse to controlling into higher G. I don't see any reference to the airplane being equipped with an accelerometer. If the G information were not available to the pilot, and his helicopter flying had not refined his "seat of the pants" sensation for G, he might not have applied enough, early enough in the dive, to recover before the speed built up. A spiral dive certainly makes sense in this situation. During flight testing, and intended dives, I've had to apply more than 2.5 G to prevent exceeding Vne (Cessna Grand Caravan). I had temporarily installed a G meter, so I could apply the required G confidently, to prevent exceeding Vne, and it worked. Without the G meter, I expect the G aversion would have seen me exceed Vne. And that was not a spiral dive, simply a spin recovery dive. The spiral would make it that much more difficult, and the moderate power on the way down would have made it all happen really quickly!
The relationship to the US and Canadian accidents appropriately shows that this was not the first time. This is a lesson worth learning! Build up unusual attitude flying skill in low drag planes with great caution!
The relationship to the US and Canadian accidents appropriately shows that this was not the first time. This is a lesson worth learning! Build up unusual attitude flying skill in low drag planes with great caution!
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The accident happened extremely quickly.
The time from the commencement of the manoeuvre at 4500 feet to the final reported altitude of 1560 ft was only about 20 seconds. A descent rate of about 8,800 fpm. The time to the accident was only 27 seconds.
it seems that these aeroplanes can run away from you very quickly.
The time from the commencement of the manoeuvre at 4500 feet to the final reported altitude of 1560 ft was only about 20 seconds. A descent rate of about 8,800 fpm. The time to the accident was only 27 seconds.
it seems that these aeroplanes can run away from you very quickly.
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it seems that these aeroplanes can run away from you very quickly.
20 seconds is lots of time to recognize something is going wrong, and apply recovery control inputs, though I agree the latter part of the 20 seconds was probably no longer opportune for any recovery effort. I helicopter pilot was probably surprised by unfamiliar attitudes, and control responses for such an agile small plane.
One point that many may not be aware of is the significance of Vne being presented as IAS and the influence of TAS. The RV has a Vne of 200kts IAS, at 10,000 feet in ISA conditions that equates to a TAS of 233kts, in ISA+20 241kts. Flutter responds to TAS. Recently read a C210 accident reportwhere the aircraft succumbed to an inflight breakup while making a high speed descent from altitude in calm conditions and this IAS/TAS disparity was given as the likely reason. DAR may wish to expand.
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Flutter responds to TAS.
I'll be test flying with a Transport Canada Test Pilot, and Flight Test Engineer in the next month, including dive tests, so I'm going to discuss this with them. Thanks for introducing the thought Megan!
AC 23-629 is the reference. Done in conjunction with appropriate analysis so the crew have some idea of the critical condition. We (myself associated with analysis so on the ground) used to estimate the start altitude so the dive would get as close as it could to what we wanted.
I recall we had a chart of achievable max IAS vs altitude in the report. The reason why the FAA warns of modifying aircraft with more powerful engines is because you’re going to get outside what had been demonstrated originally.
I recall we had a chart of achievable max IAS vs altitude in the report. The reason why the FAA warns of modifying aircraft with more powerful engines is because you’re going to get outside what had been demonstrated originally.
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Back in '74, we has a Comanche 260 in and while putting her in the hangar
medivac, I noticed a ding in the stabilator. It had been filled and faired, but I thought to check... Nothing in the logbook, so checked the static balance...It was out by a bit, so corrected that with ballance weights and passed it.
Thing was, not long before, a similar a/c had the same problem and it rang a bell. In that case, the test flight was done by the owner. To make the weight, he got some friends along...Doing the Vne part of the test, he stuck the nose down and reached the Vne while still in the dive, rather than gently pull up and reaching it in level flight.. Result was, he exceeded the Vne and the stabilator fluttered and departed. Sudden pitch down, wings folded and that was it.
I think that was the case that resulted in all C of A test flights to carried out by comercial rated pilots. The investigation found that the stabilator was out of balance due to 'hanger rash' and had been repaired without thinking it through.
Thing was, not long before, a similar a/c had the same problem and it rang a bell. In that case, the test flight was done by the owner. To make the weight, he got some friends along...Doing the Vne part of the test, he stuck the nose down and reached the Vne while still in the dive, rather than gently pull up and reaching it in level flight.. Result was, he exceeded the Vne and the stabilator fluttered and departed. Sudden pitch down, wings folded and that was it.
I think that was the case that resulted in all C of A test flights to carried out by comercial rated pilots. The investigation found that the stabilator was out of balance due to 'hanger rash' and had been repaired without thinking it through.
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Attention to detail is a large part of what makes Aviation safe. Ignoring those details can be fatal.
Regards,
Grog
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I think it's apparent why the aircraft crashed, sadly.
capngrog, the Original Poster here, quotes the report by the New Zealand CAA , which has apparently not chosen to present its data in the usual ICAO format. Would there be a reason for them not doing so?
Russ
capngrog, the Original Poster here, quotes the report by the New Zealand CAA , which has apparently not chosen to present its data in the usual ICAO format. Would there be a reason for them not doing so?
Russ
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Examples of flutter in real life and wind tunnel.
https://www.youtube.com/watch?v=egDWh7jnNic
An article on why TAS is so important with regards to flutter.
https://www.vansaircraft.com/wp-cont...1/hp_limts.pdf
https://www.youtube.com/watch?v=egDWh7jnNic
An article on why TAS is so important with regards to flutter.
https://www.vansaircraft.com/wp-cont...1/hp_limts.pdf
This article allowed me to understand why at an altitude of 70,000+ feet, the separation between V/S (stall) and V/NE (never exceed) of the U-2 is only around 5 knots. I can't imagine cruising around in the days of nuthin' but steam gauges and INS (no GPS) for hours in a U-2 flying in that narrow of an envelope. I'd be shakin' like a puppy passin' peach pits in a hail storm.
Cheers,
Grog
In the report it states the cause as flutter due to exceeding the Vne. However in the graphic of the sequence of events and location of aircraft parts the IAS of the RV was not close to Vne. The Vne was only exceeded in the later phase of the break up.
IAS at first break up location was 144kts . It was not above Vne in the preceding manouvres ?
IAS at first break up location was 144kts . It was not above Vne in the preceding manouvres ?
In the report it states the cause as flutter due to exceeding the Vne. However in the graphic of the sequence of events and location of aircraft parts the IAS of the RV was not close to Vne. The Vne was only exceeded in the later phase of the break up.
IAS at first break up location was 144kts . It was not above Vne in the preceding manouvres ?
IAS at first break up location was 144kts . It was not above Vne in the preceding manouvres ?
The New Zealand CAA has released its final report on the 01 January, 2018 fatal crash of a Van's RV-7.
Here's a link to the report:
https://www.aviation.govt.nz/assets/...ew-Zealand.pdf
Regards,
Grog
Here's a link to the report:
https://www.aviation.govt.nz/assets/...ew-Zealand.pdf
Regards,
Grog
Firstly the repeated obsession with whether the passenger was flying or not? Why is this even relevant? Experienced pilots let pax fly all the time - and with an ATPL(H) this pilot was very experienced with nearly 400hrs FW and over 4000hrs RW. It also says that he was known seldom to relinquish control anyhow. He is the captain , and should be more than capable of handling the manoeuvers in question, or recovering if his pax got into them. So why is this even being mentioned?
Secondly the conclusion of rudder flutter is far from conclusive to me in the report. The rudder was still attached to the fin, and one wing had come off. So torsional divergence failure of the wing, and/or overload due to incorrect application of rudder above Va are both in the frame. These aren't discussed. I'm not saying it couldn't have been flutter - I am saying that the investigators seem to have been a bit eager to shoot for a single explanation.
That said, that the aeroplane failed structurally in flight is clearly the case. Which brings me to another major omission in this report - any investigation of the handling characteristics and whether they (pitch stability, spiral stability being things I'd be looking at) have characteristics likely to cause inadvertent overspeed. Is there anything in this aeroplane that makes it hard to recover from a spiral dive? Is there a tendency over Vne to lock into a dive? They really should have had a test pilot looking at a similar aeroplane.
Here's another point not discussed in the report. The *correct* recovery from a spiral dive is power-roll-pitch IN THAT ORDER. I have certainly as an instructor seen a lot of pilots incorrectly applying pitch and roll together, which as an engineer I know creates a high potential for airframe overstress and breakup of the nature that happened here. Is this being adequately taught to FW PPLs? - I have some doubts, and the report missed the opportunity to ask that.
Also not mentioned in the report, is the possibility of mis-diagnosis of a spiral dive as a spin, and incorrect application of spin recovery actions to recover from the spiral dive. That would be totally consistent with the evidence presented.
Also the statement that "Flight at any airspeed over Vne, however, exposes the aircraft to the possibility of flutter." misses that flutter can be experienced in a maladjusted aeroplane below Vne. I've seen it test flying a couple of aeroplanes, even in level flight, with incorrect adjustments in the elevator and pitch trimmer circuits, one was certainly heading for an in-flight breakup if I'd not known what I was doing.
I do like the recommendation for verbal overspeed warnings in light GA EFIS. At the same time, most light aeroplanes provide loads of warnings (pitch attitude, wind noise, the ASI itself) of overspeed, which isn't mentioned in the report.
Not a happy read, on multiple levels.
G
The *correct* recovery from a spiral dive is power-roll-pitch IN THAT ORDER. I have certainly as an instructor seen a lot of pilots incorrectly applying pitch and roll together, which as an engineer I know creates a high potential for airframe overstress and breakup of the nature that happened here. Is this being adequately taught to FW PPLs?
The military pilot training and airworthiness sides are also much more joined up with each other than in any civilian environment, so it's much more possible to ensure a truly joined up aircraft approval, and pilot training syllabus than you could ever do in the civilian world. That allows you to do the sort of thing you're describing here - g-meter or not.
G
The military pilot training and airworthiness sides are also much more joined up with each other than in any civilian environment,...
We didn't have G-meters so to this day, I rarely look at the G-meter when doing gentle aeros. I use my calibrated "seat of the pants"!
The *correct* recovery from a spiral dive is power-roll-pitch IN THAT ORDER. I have certainly as an instructor seen a lot of pilots incorrectly applying pitch and roll together, which as an engineer I know creates a high potential for airframe overstress and breakup of the nature that happened here. Is this being adequately taught to FW PPLs?
MM
P.S. Most of the UPRT graduates I have talked to also fail to appreciate that the angle of attack of both wings increases as aileron (roll) is applied and that pulling to a high AOA and rolling at the same time will inevitably lead to uncommanded roll, or incipient spin. I have unfortunately witnessed with 100% consistently civilian pilots apply aileron as the first action when experiencing a turbulence (wake) induced upset in live flying.
