FL180 Cessna 172 Skyhawk
- Thread starter sdfcvoh
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jrh
Well-Known Member
I'm well aware of multi-engine performance. I know what happens after an engine failure and I know the meaning of accelerate-stop data.
What I don't understand is why a pilot would happily make a takeoff in a single engine plane that they wouldn't even consider in a twin, all because of the accelerate-stop chart.
But I have an open mind. If you care to explain yourself further, I'm listening.
staplegun
Well-Known Member
I think the difference is Part 91 vs. Part 121. I'm looking at it from a 121 perspective, while I think you're looking at it from a Part 91 perspective.
Obviously a Cessna 140 would be able to utilize a 1500' strip without considering accelerate-stop.
I flew T-34C's as an instructor in the Navy and we very rarely thought about this, either, even though on a very short runway it could bite you.
I also flew C-9B's in the Navy Reserve, and we often had to do critical field (vs. balanced field) takeoffs in order to increase our max gross weight so we could haul the pax & cargo out.
I think things are different in multi-engine even in the Part 91 world. A two engine aircraft doesn't mean you have twice the performance. Losing an engine at V1 on a 1500' strip necessitates being able to lift off (or stop before the end) with greatly reduced performance, and it will all depend on the weight of the aircraft as well as environmental factors.
Obviously losing an engine prior to lift off in a single engine aircraft makes the decision much easier, you're stopping (if you can!!) That's the difference...
I realize that the FAR's are different for Part 91 and Transport Class aircraft. I just think the performance numbers should be run, even in the Part 91 world.
JMHO, YMMV!
Kevin
CameronF
Well-Known Member
Well said.
jrh
Well-Known Member
That's been my point all along. Part 91 and 121 are two different animals and 121 is generally much more conservative.
Both are very, very safe, but 121 is (and has to be) safer.
Or any single engine aircraft, for that matter. Accelerate-stop numbers aren't computed for many single-engine aircraft in the civilian world.
And again, that's my point. I think it's goofy that a pilot would knowingly fly out of a given strip, whatever the length (500 ft, 1000 ft., whatever), in a single engine aircraft that definitely does *not* have enough room for accelerate-stop, yet they would feel unsafe doing it in a twin.
The danger is the same for either case, but the danger is more widely publicized for twins, therefore it appears to be unacceptably dangerous.
I know!
My point exactly! In the 121 world it's a limitation because frankly, the 121 world is less tolerant of risk. In the Part 91 world, certain things are more acceptable. Running the numbers is important for situational awareness, but not necessarily as a determining factor for if the flight will depart or not.
staplegun
Well-Known Member
I guess this is my point!
Why even bother to run the numbers if your going to go anyway?
Run the numbers! If they say you're good to go, then go! If they say you're not good to go, do something about it, don't just take off anyway!!!
I don't see what this has to do with 91 vs. 121...
Kevin
jrh
Well-Known Member
So you know what to expect for performance. Same reason you look at density altitude and compare it to single engine service ceiling. You might not have ANY climb performance on a single engine if the density altitude is high, but it's a lot nicer to know that and plan the departure accordingly ("if we lose an engine below 1000' on climbout we'll put it in to the corn field..."), rather than have an engine failure on takeoff and try to make the plane do something it's incapable of doing (climb).
In a single you'd be taking off anyway! Why is a twin so different?
Have you ever seen a single get the mains off the ground just in time to have the departure end of the runway whoosh underneath the belly? Well, obviously accelerate-stop numbers aren't being complied with under those circumstances, yet that's a standard, common, accepted way to fly out of a lot of tight strips in a single.
Now, think about doing it in a twin. What changed? Why is it so dangerous all of a sudden?
This all got started because I tried to explain to Seggy how there are different standards for what is considered "safe" in 91 ops versus 121 ops. The exact same activity in one area might be considered unsafe in another and it's all a matter of perspective.
jrh
Well-Known Member
Haha...ok, fair enough. A lot of pilots would, myself included.
We all have different levels of "acceptable" risk. Which again proves my point that this issue of "risk management" is a lot more grey and a lot less black and white than some people say it is.
staplegun
Well-Known Member
It's a "standard, common, accepted way to fly" because 99.9 % of the time it works out OK; but I wouldn't want to be that 1 in 1000, would you?
Nothing! Other than the different performance capabilities of the aircraft...
It's not "so dangerous all of a sudden," it's equally dangerous, just with different performance calculations/considerations...
Kevin
jrh
Well-Known Member
No, I don't want to crash, if that's what you're asking.
But I'm not afraid of doing a short field takeoff, either. That's all I'm referring to here. You're making a short field takeoff out to be some wild, risky maneuver, and it's not. It inherently has more risk than departing off of a 10k foot runway, but I consider it an acceptable level of risk.
For the dozenth time, that's my point. Risk cannot be eliminated 100%, so every pilot has to determine for themself how much risk they're willing to accept.
What's your point? Twins generally have *better* performance than singles. Of course it depends on numerous other factors, but all things being equal, I'd feel safer in a twin than a single.
Isn't that what I already said?
jrh said:
MFT1Air
Well-Known Member
He shouldn't have busted class A, everyone agrees. Why keep harping on it? Everyone with more than a few hundred hours has busted some sort of airspace.
The high altitude alone was not dangerous to himself or the airplane, nor was it illegal with respect to the airplane's operating limitations.
Mountain out of a mole hill. IMHO.
My final piece. . .
If the flight were at 17999 feet, I would have sat back and learned something about the stability and operating limitations of a Cessna at THAT specified altitude. . .fyi - I've actually learned a lot and gotten some pretty insightful viewpoints about equipment characteristics.
Secondly, FL180 with a nonrated IFR pilot? I learned what NOT to do with an aircraft, and again. . .I learned it from this forum and not an NTSB report.
A good pilot is always learning.
zmiller4
Well-Known Member
You gave the example of taking off from a field where an engine failure in either a twin or a single will result in a crash, and you're asking what the difference is between the two? You do recognize that with a twin you're at least doubling your chances of an engine failure?
If I'm assessing the risk of a flight, a 100% increase in the chances of a crash on takeoff due to engine failure certainly makes me think of things in a different light. Since the primary risk for a proficient pilot taking off from a short field comes from engine troubles, the two have distinctly different levels of danger.
The emphasis of the thread ought to be that the OP 1) busted airspace because he wasn't aware of the entry requirements and doesn't appear to care very much, and 2) made a concious decision to intentionally push the limits of the aircraft without having anywhere near the experience to know the risks involved. TonyC was exactly right.
Seggy
Well-Known Member
staplegun
Well-Known Member
You and I are talking about apples and oranges here...
Obviously single engine aircraft always have the risk of losing the engine in any regime of flight, that's a given and really shouldn't be part of our discussion here. I'm only talking about takeoff performance.
In a single engine fixed-wing aircraft, V1 almost always equals Vr. In other words, if the engine quits prior to rotation you're going to stop on the runway, if you have room.
In a multi-engine fixed-wing aircraft, V1 and Vr are not necessarily the same. If one engine quits, the pilot has a lot of complex decision making to do in a very short amount of time. The point in the takeoff roll where the engine quit is what drives those decisions; why wouldn't you give yourself an out? That's what multi-engine is for!
This is the one that got me going. I understand that the single engine pilot feels he has nothing to lose by doing it this way, because either way if his engine quits he's along for the ride. That's the risk you assume by flying single engine. Although I personally would like to have enough room to stop if my engine quit prior to Vr!
You asked what changed by making the aircraft multi-engine. The whole point of multi-engine is to use the increased performance of the two engines to set yourself up so that you don't get into this predicament. The whole reason to have another engine is so that you will survive this scenario, and the only way to do that is to give yourself adequate accelerate-stop distance on the runway. If all your doing by flying the twin is ignoring the safety margin it can give you, then don't bother flying it! Get a big, high-performance single and stick with that!
My point is that along with the increased performance of a twin comes an implied obligation to utilize it correctly. You would only be safer in a twin if you allow the aircraft's performance to keep you alive when you lose an engine! That's why I say this has nothing to do with Part 91 vs. Part 121.
Kevin
jrh
Well-Known Member
I have a huge amount of respect for staplegun, and I have been listening. That's why I said this:
As for the 91/121 stuff...yeah...that only served to distract from my ultimate point that risk management is a very grey area. I didn't mean for it to become a debate in and of itself, and I wish I'd used a different example.