Quote:
Originally Posted by Timbo
What happened in most of the hard landings was, they were on short hops, then came down from altitude very quickly so there was fuel trapped in the horizontal stabilizer, which gave them an aft CG, but they weren't paying attention to the CG, even though it is indicated right there on the EICAS.
Being a former KC135 guy, I was very much aware of the CG, all the time. When I got on the MD11, I asked why there were no limits for landing, and 'what if' it got too far aft?
"That'll never happen..." was about all they ever said, then they just kept crash landing them...
Did they at least fix the fuel management computer so it will run all the tail fuel fwd regardless of altitude? I can't recall the exact number but I think around 17,000' all fuel shifting would stop, so if you came down from say 350, very quickly, you would go through 17 (or was it 19?) and there would still be fuel in the tail...which you couldn't move forward, and you were stuck with an aft CG for landing.
You got some of the numbers right. And yes, I'm guessing there has been some tweaking over the years because TFM (tail fuel management) issues really aren't that big a deal now.
There is no TFM unless your fuel system is able to run in auto. In manual mode, no TFM. If auto fails in flight and you revert to manual, all TFM stops and the fuel transfers forward.
In order to activate TFM, you have to have more than 60K of FOB at the end of refueling. It stops any further aft transfer at 51K FOB. So, short hops aren't a factor unless you're tankering gas.
The tail fuel is sent forward when any one of the 3 main tanks hits 11.5K to keep all three tanks at that level until tail is dry (so, roughly 35K+ 13K of tail fuel = 48K FOB it begins)
No matter what, ALL tail fuel begins to get transferred forward on descent passing about 27,000 feet. The only way it stops transferring forward and becomes "trapped" in the tail is below 18,000 and dirty (any one of slats, flaps, gear).
In practice, the only time getting fuel trapped on descent might be an issue would be an air turn back or tankering scenario. Even then, you'd probably have to put the slats out VERY early to trap the gas. I've gone through 27,000 with a full tail tank just starting to transfer forward and it's empty by the time we get below 10K.
IMO, this is a great airplane. I've flown three 2-engine Boeings and the A319/320. The systems on the MD-11 are head and shoulders above those other jets. Part of that is just due to the redundancy available from a third engine. But the system interface, displays and operation are truly superior as well.
I also enjoy the way it flies. You can click everything off and fly it just like any airplane. I flew it for two years before I heard anyone tell me how hard it was to land. Yeah, a pilot probably can't get away with some of the ham-fist stuff that passes muster on a 777 or some other Boeing. So, you bring your A-game (like everyone should anyway). If that's too much to ask, then I guess the 777 is the obvious choice. As Dirty Harry said: "A man's got to know his limitations".
But, really it's all the old basics: Use power properly on final and in the flare and make adjustments based on your landing weight, land on centerline, de-crabbed, at the correct pitch and don't fix a sinker with pitch. Those rules have pretty much worked with any jet I've flown (except F-15s and T-38s didn't de-crab).