Light plane crashes

[BoeingBobby]

"There I was, the sun was in my eyes. I knew that the Messerschmitt was hiding in it above me."

[kent olsen]

If I read it correctly this a/c was based at Gillespie. They were returning from a quick trip up near LA. I was a flight instructor at Gillespie between 1970-1973. There's a little hill south of the extended centerline and a tall one on the north side. Couldn't tell from the report where he hit the ground.

[Gabriel]

VAS aviation:
https://www.youtube.com/watch?v=lIjMCPKULMM

Maximus (Note, this one includes the harrowing screams which you may find emotionally disturbing, as I did. Some may not want to listen to this version. Listen at your own risk).
https://www.youtube.com/watch?v=jpsvGPPQxyo

Kathryn's report (a collection of facts and sources, not a video)
http://www.kathrynsreport.com/2021/12/l ... ident.html

Blancolirio:
https://www.youtube.com/watch?v=lalLdpFAryI

Dan Gryder. In general don't like Dan at all but in this case he has good factual data, and in this instance I also generally agree with his analysis and opinion.
https://www.youtube.com/watch?v=8pS17RPgqfI&lc
EDIT: Dan's video was taken down, or rather made private which has the same effect of not being accessible. No idea why. It is a pity, it had good ASD-B data graphed in 3D over 3D google maps with terrain.

This is the new video (1/7/2022) that replaces the one Dan took down: https://www.youtube.com/watch?v=hX8V0WCWllM

[Evan]

Overall, doesn't seem like a particularly "jet-friendly" airport.

According to Wikipedia, of the 547 aircraft based there, 3% are jets (which would be 16 and one half jets).

[ATLcrew]

Gillespie seems like an "interesting" airport. The only runway authorized for Cat C or D aircraft is runway 17, which, at 4,100 feet, seems awful short for most such aircraft. For 27R the only published approach is LOC-D (see chart) which has no straight-in minima and for good reason: the glidepath from DEBEY to the runway is almost 7 degrees (one would have to lose 2400' in 3 miles, or, a the scientific term is, a shitload of altitude). I'm not real clear why 9L is not authorized for Cat C or D, perhaps because there is not enough room for a missed approach turn at Cat C or D speeds. There appears to be terrain at 1273' between DEBEY and the runway, so not much maneuvering room even in the best of conditions. Overall, doesn't seem like a particularly "jet-friendly" airport.

[BoeingBobby]

So do I. You lose 15 knots of airspeed, you'll have 96 knots. Next what?

Why were you so slow to begin with? If they are reporting -15 on final???

[Gabriel]

Pilots are supposed to be trained to then factor in wind additive and, of course, to then fly a margin of safety above the result to account for such things as [bunch of things]

No, pilots are trained to look up one speed and then add the wind additive. The look-up speed should already contain all the other margins. The pilot is not expected to figure out the margins.

[Gabriel]

Not sure I follow you. 102kts is the manufacturer-provided number for the aircraft in a level 35 deg turn without any wind additive. Pilots are supposed to be trained to then factor in wind additive and, of course, to then fly a margin of safety above the result to account for such things as gusts, the elevator inputs as described above, turbulence from passing meteors and anything else that might be unexpected. In other words, never fly at the edge of the envelope. What is the NTSB saying that condradicts that training?

Ok, I misread that. I thought that 102 was the 1G stall speed. But if 102 is for a sustained, coordinated, constant vertical speed 35-degrees-bank turn, for 1G it would be 93 kts. And 1.23*93=115 which would be one of the minimum bounds for Vref. So now a Vref of 119kts makes more sense.

[Evan]

I don't like how the NTSB typically talks about stall. Do you know what happens if you are flying at 111 knots when the "official" stall speed is 102 knots, and get a sudden negative-15kts-gust?

Not sure I follow you. 102kts is the manufacturer-provided number for the aircraft in a level 35 deg turn without any wind additive. Pilots are supposed to be trained to then factor in wind additive and, of course, to then fly a margin of safety above the result to account for such things as gusts, the aileron inputs as described above, turbulence from passing meteors and anything else that might be unexpected. In other words, never fly at the edge of the envelope. What is the NTSB saying that condradicts that training?

[Gabriel]

Yes I do

So do I. You lose 15 knots of airspeed, you'll have 96 knots. Next what?

[Gabriel]

Vref has to meet 2 lower bounds:
a) 1.23 Vs (23% above the stall speed), which is good for 1.5G before you stall, which in turn is good for a sustained, coordinated, constant vertical speed turn of more than 45 degrees of bank.
b) Be able to sustain a coordinated, constant vertical speed turn of 40 degrees of bank without a stall warning. The load factor in such a turn would be 1.31G which would increase the stall-warning speed by a factor of 1.14. At the same time, the stall warning at 1G needs to occur at least 5% above the demonstrated 1G stall speed.
Since 1.15*1.05=1.2, unless the stall warning has more than the required 5% margin over the stall speed, a) would be the limiting factor.

I think that that speed (+ wind additives) is ok as a final approach speed. But not for maneuvering (i.e. when you still have turns to make).

My reasoning is as follows:
1- Forget about the stall speed. The stall warning speed is the absolute minimum, not as a reference speed, but after considering all factors that add variation. The activation of the stall warning would need you to stop whatever procedure you were following and initiate immediate recovery. All operative margins must be on top of the stall warning, not on top of the stall. The only thing with a margin on top of the stall should be the stall warning itself, which is a factor of 1.05 as we said (when the stall speed is above 100 knots, if it is below the minimum margin is 5 knots)
2- You need to account for corrections of the flight path. If you find your self a bit too low (say 1 dot low in the ILS, 3 red lights in the PAPI, etc...) you will need to reduce your descent rate and for that you will need a load factor of more than 1 and for that you will need to pull up a bit and increase the AoA (unless you increase the speed and let the increased speed increase the load factor without increasing the AoA, but that's not what you want to do if you are already at the target speed). I arbitrarily take 1.22G as the allowance for vertical corrections of the flight path, just because it seems reasonable and the sqrt(1.22) is 1.1 which is convenient.
3- You are not established on final yet, you need to turn. Let's say that you commit yourself to 30 deg turns. Ok, but how good ae you at keeping 30 degrees? Let's ad +/-5 degrees for imperfect pilot accuracy. A sustained, coordinated, constant vertical speed, 35-degrees-bank turn has a load factor 1.22G which, very conveniently, translates to a speed factor again of 1.1.
4- And, again, when I am doing a 30 degrees turn that accidentally went to 35 degrees and I need to do a correction in the vertical flight path, I STILL DON'T WANT THE STALL WARNING TO SOUND, so give me a 10% margin over the stall warning.
Combine all that and you get Vs*1.05*1.1*1.1*1.1=1.4Vs (if the stall speed is 100kts or faster, if it is lower it would be (Vs+5kt)*1.1*1.1*1.1).

So if the stall speed is 102 knots, as in the Teterboro example, the Vref would be 102*1.23=125kts (not sure where the 119 came from), and that may be ok once established in final, but if you still have maneuvering (turns) to get to final, you should keep 102*1.4=143kts until established in final.

This may seem excessive, but if you want to go slower, tell me in which of the above factors you are willing to give up and by how much. And why. Because the best intentions won't beat Physics.

As a side note, the same calculation leads to a minimum maneuver speed of 70 kts in the Tomahawk, which is exactly what we used in the pattern until established in final.
The manual says that the final approach speed is 62 knots, which is about right for the Vref margins. And my instructor could never tell me why we used 70 knots instead, other than "62 knots is too slow regardless of what the manual says". Now I have a better justification.

[BoeingBobby]

I don't like how the NTSB typically talks about stall. Do you know what happens if you are flying at 111 knots when the "official" stall speed is 102 knots, and get a sudden negative-15kts-gust?

Yes I do

[Gabriel]

I don't like how the NTSB typically talks about stall. Do you know what happens if you are flying at 111 knots when the "official" stall speed is 102 knots, and get a sudden negative-15kts-gust?

[BoeingBobby]

Angle of bank, pulling up, ie added G force, who knows what his CG was, all add up to a higher stall speed. I can get the Pitts to stall at 120 knots to get it to enter an inverted flat spin.

[BoeingBobby]

Look up the definition of accelerated stall.