From: rdd@cactus.org (Robert Dorsett)
Subject: Re: A320/automation: forwarded from the aero list...
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date: Thu, 30 Jul 1992 01:39:19 GMT

In article <92211.134130TXK9@psuvm.psu.edu> TXK9@psuvm.psu.edu writes:
>Doesn't this crash of 320 sounds very much like the one of Indian Airlines
>flight which crashed in Banglore, India? The pilots didn't live to tell the
>tale. However I read a report which showed that Pilots did realize that the
>plane was losing the height too soon and try to activate manual throttle
>control, but the response time for the engine being slow (compared to
>fighter aircraft or 747 I am not sure)the plane could not recover and landed 
>short of runway. Does anyone remember any other report of this crash?

There are few overt similarities between the Habsheim and Bangalore crashes.

1. Habsheim was an airshow flyby, dirty, engines at idle, losing airspeed;
the airplane probably flew into the trees because the pilots had poor 
altitude awareness, and, due to the nose-high attitude, couldn't see
the trees they were flying into (they were that low).

2. The CFM-56's on the Habsheim airplane *may* have been one second too
slow when spooling up to full power.  Airbus/CFM subsequently introduced a 
guide-vane modification to guard against possible stalls in high angle-of-
attack configurations.  But, again, the DFDR doesn't support the idea that
this was a contributing factor at Habsheim; the much-ballyhoed "bangs" were
probably the sounds of the tail striking the forest canopy.

3.  The engines on the A320 spool up at about the same speed as comparable
engines on comparable airplanes, including CFM-56 variants installed in
the 737-300/400/500 series.  The -56 is a "small fan," as opposed to a 
"large fan", and probably spools up *faster* than the sort of engines 
installed on a 747.  The spool-up speed was almost certainly not a factor,
and is not a point of contention.

4.  The Bangalore crash was during a revenue approach.  The crew were flying
a revenue approach to Bangalore.  A check-captain and a new captain were 
flying the airplane.  The crew noticed they were a bit too high, and 
apparently engaged the "open descent" mode on the FMS (Expedite button),
which commands both a high AOA and full throttle-back.  They ignored at 
least one ground proximity warning alarm, and apparently only started the 
recovery at 135' AGL.  

The interesting thing here is that the commander relied on the protections, 
even then, to save his bacon--he pulled full-back on the stick, to engage 
alpha-floor protections, *then*, two seconds later, commanded full-thrust 
with the engines.  This is strongly indicative of the *strength* of 
Aeroformation's "rely on the automation" training, IMHO.

The report notes that if the throttles had been advanced FIRST, as would be 
the natural "instinctive" pilot-response, they would have gotten an additional 
three seconds of spool-up time, which could have been very significant in 
helping to avoid the crash.

As it was, the airplane augured into a golf course embankment, coming to
rest a few hundred meters short of the runway.  The airport crash vehicles
were locked into the compound, and couldn't get out the gate, which undoubt-
edly worsened the death toll.

The above is based on Sections 2 & 3 of the crash report; I don't have
the Bangalore DFDR or prologue.

It's worth noting that 

(a) Some industry publications initially speculated that the FPA mode, 
which has been seriously discussed as a factor in the Strasbourg crash, 
had caused the Bangalore crash.  This wasn't the case: a different mode 
had been engaged.  

(b) The "low-energy" similarity to the Habsheim crash extends only to the
late time at which the crew realized their predicament.  

(c) Airbus was under heavy criticism in India, after the crash: the popular 
press played up every A320 horror-story they could get their hands on.  The 
fact that the 737 was dropped in favor of the A320, at a very late date, led 
to allegations of corruption of senior airline and government officials.  
This *might* have influenced the tone of the final report, which is more 
critical than the Habsheim report, but Airbus formally concurs with its 
findings.


So, overall, the main differences are that at Habsheim, the airplane was
under *manual* control, flying a flat profile, very close to the surface.
What happened next is familiar to any student pilot practising "power-on
stall" maneuvers at a constant altitude.  At a certain point, one simply
doesn't have the power to maintain altitude, and a "break" (the stall)
causes the nose to pitch down, and altitude is lost, until airspeed 
increases again.  

At Bangalore, the airplane was in a high-AOA, *steep* descent, with 
engines at idle.  The end result is much the same.





---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd
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