Text 19361, 112 rader
Skriven 2008-08-02 09:48:19 av Ward Dossche (2:292/854)
  Kommentar till text 19345 av Michiel van der Vlist (2:280/5555)
Ärende: Re: Immigration
=======================
Michiel,
 
Mv> It wasn't the first time this happened with this type of aircraft. In
Mv> France a few years earlier a 747 also lost two enigines on the same side
Mv> due to a failing pin. By an incredible combination of skill and luck, the
Mv> pilot managed to put it down on a runway without anyone getting killed.
 
That pin is designed to desintegrate when certain stress levels are surpassed.
The purpose is to jettison the engine without causing structural damage
in-flight. This is exactly what happened. 2 engines dropped without structural
damage to the control surfaces so the plane was still an aerodynamically sound
plane. The checklist provides for maneuvers with 2 engines out on one side,
pilots train for that.
 
In the Bijlmer it was different. #3 engine damaged the leading edge slat which
had already been retracted and could not be extended anymore. It also damaged
the pylon supporting the flaps.
 
So when the 2 engines broke-off, slats and flaps had been retracted, the plane
was flying in excess of 280 knots and because the wingsurfaces were undamaged
there was adequate lift.
 
The plane radioed it had "lost 2 engines", meaning they were out of order. From
the cockpit of a 747 one cannot see the engines and the crew had no indication
the engines detached. The aircraft could have remained airborne on the 2
remaining engines, however it is very unlikely it would ever have landed safely
in whatever configuration. The reason therefor was that when reducing speed in
preparation for landing, the slats and flaps are extended to increase lift at
lower speed. This didn't work on the right wing so when the aircraft slowed
below critical speeds in preparation for landing, the right wing stalled, i.e.
lost lifting power, and dropped down. As a result the aircraft went down with a
90ø right attitude without chance of recovery.
 
Minimum speed to remain airborne under that condition was 280 knots. A fully
loaded 747, even with empty tanks, will not survive a landing at such speeds.
Second, with only 2 engines for thrust reversing it is highly unlikely it would
not overrun the end of the runway.
 
Once I was in an emergency landing of an Embraer-120 Brasilia, that's a 27
passenger propjet, in Brussels. A no-flap landing meaning you were landing at
minimum flight speed. That small plane needed about 3.000m to brake to a stop.
A 747 would never make it.
 
Mv>WD> Nearly exacly the same case as the American
Mv>WD> Airlines DC10 which crashed at Chicago O'Hare.
 
Mv> Apples and Oranges. The DC10 had all the hydraulic lines on the front of
Mv> the wing. The (one) ripped off engine caused all three independent
Mv> hydraulic systems to fail making the plane totally uncontrolable. It
Mv> rolled right after take off and crashed immidiately.
 
You could have been better informed.
 
When the hydraulic line on the port wing was severed, it caused immediate
auto-retract of the leading-edge slat. The plane was already at V2 and
rotating, took-off and power was increased, the flight would have been normal.
In the cockpit however there was a warninglight for engine-fire, so the
checklist called for fire-fighting, shutdown of the engine, reduce speed,
go-around and land. That would have worked had the slats been extended which
the captain assumed (at that time there was no indicator on the instrument
panel).
 
When according to the McDonnel-Douglas handbook the speed was reduced the port
wing stalled, i.e. lost lift and as a result rolled LEFT (not right) crashing
in a 190ø attitude.
 
Both planes could have survived had the proper information been available to
the pilot. The DC10 certainly would have landed safely, the 747 would have
crashed upon landing.
In the case of the DC10 it was again one of its famous design flaws resulting
from a too speedy programme to catch-up with Boeing's and Lockheed's wide-body
programme. Boeing and Lockheed in all of their planes, as well as
McDonnel-Douglas except for the DC10, needed hydraulic pressure to retract
slats, so when pressure would drop for whatever reason the slats would still be
in place..... No pressure = slats extended ... in the worst case excessive
drag.
 
In the DC10 pressure was used to extend them and keep them in place. So when
for whatever reason pressure dropped, the slats would retract out of control of
the pilot without a slat-indication and the planes ability to stay airborne at
lower speeds would be compromised.
 
After the Chicago-crash all DC10's worldwide had to be modified and after the
initial problems with the accident in Ermenonville it signalled the beginning
of the end of its commercial carreer though a number of the modified planes
eventually went beyond 100.000 hours. The MD11 never managed to clear-up the
smoke, it was a complete new design but looked too much as a DC10 and when
Swissair lost that plane at Peggy's Cove many were retracted from passenger
service and converted to freighter.
 
It is in any case wrong to state that the Chicago DC10 was uncontrollable.
 
Mv> In hindsight, the pilot should have ditched it in the IJssel lake. Then
Mv> there would have been no casualties on the ground and the crew might even
Mv> have survived.
 
I doubt the survivability of the crew and the non-revenue passenger in any
landing and, of course, with hindsight everybody is an expert.
 
Mv> The pilot might have attempted that had he been aware of
Mv> the extent of the damage, but it is my understanding that he was not even
Mv> aware that two engines had come off.
 
Indeed. The crew merely thought the engines stopped functioning. Nowadays
planes are being outfitted with a videocamera in the top of the tail sending an
image to a screen in the cockpit showing most of the fuselage plus
wingtip-to-wingtip with a clear view of all engines on the wing.
 
 \%/@rd

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