Re: SR111: Reality check please

Date:         13 Oct 98 02:48:21 
From:         Alan Browne <alan.browne@SPAMX.sympatico.ca>
Organization: Bell Solutions
References:   1
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JF Mezei wrote:
> I have seen some news-releases from US law firms stating that the MD11
> is capable of an emergency descent at 6000 feet per minute. Can anyone
> confirm this ? If the 6000 number is not accurate, please substitute it
> with the proper number in subsequent questions.
>
> When a pilot is told that the threshold for a runway is X miles away,
> does this mean that the pilot must plan to be at altitude 0 at the
> threshold ? If not, how high must he be ? and how far would that
> threshold be from the actual runway ?
>
> If one is to make an emergency descent at 6000 feet/min, how far from
> the threshold (and how high) must he level the plane to make final
> approach ?

6000ft/min descent is possible, but I think you would end up at a great
deal of knots and have to spend some distance bleeding the energy off.
Also, from a pilots point of view, are you going to take a difficult
situation and make it more difficult by adding a manouever that loses
alt while increasing speed drastically?  Emergency management means,
among other things, keeping the variables down.

When setup for the final approach, let's say 5 miles back of threshold
(aprox 1600 ft alt above threshold) the aircraft needs to be at its
approach speed (less than 200 kts, more like 140-160), so any speed
accumulated during the mad dive needs to be dissipated before that
point.

During the mad dive, the pilot *could* dirty up (wheels, slats, flaps,
spoilers, landing lights, RAT) to increase drag.  What degree does the
MD-11 system allow the pilots to manually do this?  I don't know.  What
airspeed would result?

Further, the pilot wanted to dump some large amount of fuel.  This takes
time and distance to accomplish.  It is neccesary in order to have a
safe landing weight.  If the aircraft structure failed on landing, then
the fire hazzard would be enormous.

I noticed in AW&ST that the controllers wanted (the transcript and a/c
position plot imply this) the aircraft out over the water before the
fuel dump began.  This may prove to have been costly in the time
evolution of the event.  Where is this vs. altitude?  Don't know.

Question:  is dumping fuel really neccesary in such an emergency?  Fuel
dumping occurs more often than one might suspect.  eg: after takeoff an
inertial fails and the MEL for the flight says gotta have three.  So you
dump and go back.  But in an emergency such as Swissair 111, would it
have been safe to land fueled up, allowing that the aircraft would have
required a very expensive inspection and possibly major repairs?  Or
would the high weight have guaranteed a massive structural failure?

> During a descent, how fast can an MD11 go in terms of airspeed ? During
> an emergency 6000ft/min descent, how slow could that plane go ? How long
> would it take to slow the plane from its descent speed to a speed
> acceptable for landing? (in time or distance units).
> - - - - - - -
>
> We know that the plane was "viable" between 22:15 and 22:26, roughly 11
> minutes between the time the pilots started to act on Halifax and the
> time the electrical system failed. We also know that the plane was able
> to sustain a certain level of control after that (from the fact that the
> plane made a tight circle - is that a correct assumption ?).

The "tight circle" after departing land towards the ocean may have been
a spiral dive.  Was the XPRDR operational during this period...do we
know the altitude change during the "tight circle".
A spiral dive is easy to get into in any airplane when reference to the
horizon is lost.  In a smokey cockpit at night...

(I don't know this to be the case with this flight.  The 737 crash in
Central America a few years ago was due to the pilots following a failed
VG on the ADI.  Both pilots were switched to the same VG because the
other VG was failed.  The crash was definitely a spiral and very fast.)
<<Snip>>

Alan. (more questions than answers, as usual)