Jim_B, I seem to remember a 747 that took off from IAD about 10 years ago losing an engine and landing back at the airport safely. I'll try and find some documentation of this tomorrow...

msn, I think you are right, I am getting V1 and Vr mixed up. I think the Boeing tests I've read about involved shutting down engines at Vr...

Our pilot today at arrival into ORD told us about the AA flight and told us that a two engine jet is engineered to fly on one engine.

I'm surprised B747-4325456953B hasn't replied yet...

A twin engine plane is designed to fly safely on one engine. This is because at cruise, a plane only uses about 15% of available engine power (from each engine), or in the case of a single engine, 30%, the rudders making up for the yaw moment from the thrust differential. Similarly, it can land with one engine as well, because lets be honest, how often do you land a plane at full throttle? But, if an engine unexpectedly shuts down/falls off/explodes during takeoff, with no rudder deflection, the aircraft will very quickly yaw and roll to the side of the unpowered engine, and pitch downward. The resulting dive is dangerous because, not only is the plane suddenly moving rapidly toward the ground, but also, since the plane is canted to the side, not all of the lift produced by the pilot pulling back on the stick is converted into upward rotation (some of it causes the airplane to move horizontally). Thus, it takes a lot more elevator deflection from a possibly damaged hydraulic system to right the aircraft. When you're only 1000 ft off the ground, the result is what happened today.

As far as differences in aircraft design go, it really doesn't come significantly into play on a twinjet in this situation. Any two engine aircraft (engines mounted mid-wing) will exhibit these dynamics if it is faced with a catastrophic engine failure while at high power. Design mainly comes into play when dealing with the less severe scenario of a catastrophic engine failure while at cruise altitude and power.

And to think I was lurking here to take a break from my aero homework .

Edited to add content.

[This message has been edited by terradevil (edited 11-12-2001).]

The root of the problem with the DC-10 crash at ORD was probably the way its flap and aileron control cables are were routed.

DC-10 engines were (are still?) held on by three bolts, two forward and one aft. If the rear one fails, the engine rotates around the forward ones: forward and up, crushing the leading edge of the wing. On DC-10s that's where the control cables are, though in most other jets they're behind (and protected by) the main wing spar.

Were it not for this, a DC-10 with two functioning engines and the third physically missing should be able to fly enough to get back on the ground safely. The amount of structural and aerodynamic damage that would accompany any engine falling off, and whether the crew would have been able control the dive before they hit the ground, makes it speculative as regards whether that specific situation would have been survivable with a different control layout.

Several DC-10 quality issues have been traced to intense pressure by McDonnell-Douglas management to beat the 747 to the sky - their mantra was "Fly before they [Boeing] roll." However, I don't think that was a factor in this. It takes no longer to design cables aft of the main spar than it takes to design them inside the leading edge of the wing.

All very possible. Rear-mounted engine a/c such as the DC-9 can tolerate the physical loss of an engine loss better than wing-mounted engine a/c. Sometime in the past 10-15 years, a DC-9 family a/c (either a DC-9 or M-80) lost power in an engine. The a/c made a routine one-engine-out landing and only after landing was the lost engine noticed.

I'm also curious to what extent the fact that an Airbus 300 jet is completely fly-by-wire may have played a role. As far as I know, Boeign jets are still designed with actual physical control equipment that lead from the cockpit to the control surfaces.

Of course, these are still hydraulics aided, but it's possible for a pilot, with enough leverage and strength, to control the flaps even if the hydraulics and computer systems are down.

A fly-by-wire aircraft can't do this if there's computer damage. The pilot's harness is connected only to the computer.

Now, I know the above argument was made when the F-16 was introduced, but what may be true for a 1-2 person fighter jet may not be for a large widebody commercial jet. You may need to be Superman to actually control the aircraft without hydraulics aid.

Any thoughts?

The statement that losing one engine while both are under full power will render the aircraft uncontrlable is incorrect. With no other damage it will fly fine. In fact, on modern aircraft the autopilot even takes care of the yaw.

All Boeing airpline being able to fly with engine loss at V1 is correct for all their transport planes. In fact, all Part 121 certified aircraft are required to be able to do that at max gross weight. Part 121 certification is required for all aircraft approved for service with over 19 passengers. Yes, even most those prop powered commuter planes will do it.

Take off is only aborted BEFORE reaching V1 (otherwise known as commitment speed), V2 is the speed the aircraft is at when the main wheels leave the ground, Vr is the speed the nose starts being picked up (rotation speed). A demonsrated V1 "cut" is required at certification for all Part 121 aircraft and pilots have to demonstrate their ability to fly out of a V1 cut during type certification and usually during recurrent training (every six months).

And finally, it is true that a three engine plane may fly on only one engine, but it is doubtful that it could climb or go around on approach even under ideal conditions. But one will get you safely to a nearby airport unless there's a mountainess obstruction in the way.

Tis doesn't even factor in. The A300 and shortened derivative, the 310, are not FBW.

A twin-engine airliner CAN safely fly if an engine falls off (or just quits) provided the wing / flight controls are not damaged too much and the crew performs correctly (UA almost lost a B747-400 last year when one engine failed on takeoff at SFO. The crew did not use correct flight control inputs and nearly hit the hills to the west of the field). The pylons (what the engine is mounted to) are designed to "break-away" from the wing cleanly - this could be caused by severe turbulence, an un-balanced engine, internal damage, bird strike or any number of situations.

As part of our training, we practice engine-out manuevers numerous times during our semi-annual simulator sessions. Granted, we don't practice an "engine falling off". However, we do practice hydraulic system failures (single, dual, and complete failures - like UA232 at SUX), fires, electrical system failures, flight control failures (flaps, slats, rudder, elevator, trim and even complete flight control failures), etc. We even practice multiple system failures at the same time.

There are three different situations here.

1. Engine failure. Every multi-engine aircraft, not only commercial jets, is designed to fly, maneuver (perhaps in a restricted sense, especially as regards turning toward the side with the most remaining power) and land safely with one engine out. Pilots are trained to handle this situation.

2. Engine removed. In the totally hypothetical situation that an engine were designed like a drop tank, so that it could be physically released with no other damage to the aircraft, most multi-engine aircraft should still be able to fly and land. To my knowledge nobody has ever designed an airplane with quick-release engines (other than a few special-purpose takeoff assist rockets). I'm certain no commercial jet has them.

3. Engine falls off. Here the problem is that, if an engine that wasn't meant to fall off does, it will cause a lot of airframe damage in the process (or there was a lot of airframe damage that made it happen). It's this damage that creates the largest share of problems, not the lack of one engine's power or even the lack of the engine itself.

Unfortunately, the recent event was a #3.

RE: #2 The A10 Thunderbolt "Warthog" GE Turbofan engines can be jettisoned by the pilot using explosive bolts.

RE: #3 This is going back a while, but I thought that commercial jet engines were designed to shear off if the engine threw blades. Otherwise, like an off-balance washing machine, even a minor imbalance could precipitate a structural failure in the wing.