Question for the pilots - do you get nervous flying commercial?

dmark1 · Mar 26, 2009

solofast said: ↑

Mark, you have a million more hours than I do, and fly for a living most days, so I am sure that you are far better trained and have more pilot experience than I ever will. I'm coming from my experience as an engineer, and one who has experience taking an engine through an FAA cert program, so I tend to look for anything that can happen and then assume that it absolutely will, and then look at what will happen WHEN it does. Believe me I have seen some bizarre failures and things that one would simply think were not possible. But the end result was a hole in the ground and people in body bags.

First, using your statistics for engine failure, there were over 400 engine failures and 78 engine total engine failures last year in the US commercial airline fleet. That's about one a day, and about three "total" engine failures every two weeks. You may fly your entire career and never experience one, but it happens. I have over 30 years designing, developing and maintaining turbine engines, know them intimately, and, maybe because I've seen a lot of twisted metal, I am more aware of the damage an uncontained engine failure can wreak on an airplane. While it may never happen to you, you specifically train for that event because it happens often enough. I have been on one commercial airline flight that had in-flight shutdown, and on one that had an uncontained failure during takeoff and I don't fly much at all, typically once or twice a month. (note those were both JT8D's and thankfully there are less of them around nowadays)

As far as margins go, I am not contending that there are no margins in these actions. Yes absolutely you are at 1.5 x Vso during climb, and if you lost an engine you would just put the nose down and go about your business. If you loose a slat, your stall speed isn't Vso, it's Vs1. If you are in a high aoa climb you could very well be BELOW VS1 (I looked up the typical climb speed for a 747, and early climb was at 180 kts, while Vs1 is 198 kts at max weight, take a look at your POH and let us know what the Vs1 is for your aircraft and let us know what you climb at, that's your margin, for the loss of a slat, I guarantee it isn't 1.5). So if you loose a slat for some reason you may very well be significantly BELOW stall when it happens. If the 747 example is correct (and since I found those speeds on the internet, I can't assume they are) if you lost a slat and were 18 kts below stall, I don't care how much of a hot rock you are as a pilot, the airplane stalled a long time ago. And remember the stick shaker/pusher doesn't know anything about a degraded airplane so you get no warning. If you lost one slat at a speed below Vs1, the airplane would roll and you would have absolutey no control over it.

The point is that you are quoting margins on the airframe that you and the good folks at Boeing assume you have. If you lost a slat and don't have that airplane, you could very well have less than no margin, and in any case it is a heck of a lot less than 1.5. The guys taking off in Washington DC had a load of snow on the wings, they flew the airplane by the book and it went down on the GW bridge. As noted previously, when the AA DC-10 lost the slat on the left wing, he slowed down to pattern speed, assuming that he had an airplane that could fly with margins at a Vref that was 1.5 VSO. He died. The guy taking off in the DC-9 in Detroit thought he had the flaps at the takeoff setting. He didn't and he died. These are but three examples, with something like 400 dead people that resulted from flying an airplane that didn't have book performance, by the book, and right into the ground.

Prudent margins aren't based on a simple number like 1.5, they should be based on what can and has happened. I'm confident that 99.999% of the pilots that "shoot for the moon" on takeoff don't think it is a risky maneuver, and will never have a problem doing it. But all it takes is once, and I hope that I'm not on the aircraft when something like this happens (note here I didn't say if, because it already has at least once, which at least proves it is entirely possible) .

That's why pilots that shoot for the moon bother me.

Happy landings...
Click to expand...

Extra airspeed = Less altitude. Less altitude= less rock clearance. I will take my chances (and dare I say MOST everyone else would also) on a one in a billion chance that you would BOTH have an un-contained explosive engine failure that would
take out a slat that would cause a stall (all in a period of less than 2 - 3 seconds that it would take a pilot to recognize and lower the nose to pick up airspeed) rather than have plenty of obstacle clearance altitude at EVERY takeoff.

Your logic states that doing something that is "not in the book" is safer than what millions of flight hours, testing, pilot training, AND Boeing engineers say is correct "by the book"

Not on my watch.

Best Regards

Mark

Paul N · Mar 26, 2009

When I'm not PIC , I keep my comments to myself.

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Question for the pilots - do you get nervous flying commercial?

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Question for the pilots - do you get nervous flying commercial?

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