Re: A brief commentary

From:         Mark Ingram <markt@mickey.mo-net.com>
Date:         20 Jul 96 15:59:10 
References:   1
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On 16 Jul 1996, Glenn Carroll wrote:

> Alright, I now know well enough why the captain decelerated to V2, but none
> of the answers have done much to enlighten me about the substance of the
> question.  V2 is the speed one is supposed to fly with one engine out.

V2 is "Takeoff Safety Speed."  That is "the actual speed attained at 35
feet above the runway surface with engine failure at V1 [Critical Engine
Failure Speed, i.e., Decision Speed] and the airplane rotated at VR.  V2
will always be *at least* 1.2 VS [Stall Speed] ... and varies with
weight." (emphasis added)

"VR [rotation speed] is the speed (IAS) at which airplane rotation is
initiated assuming a continued takeoff after engine failure at V1 speed.
When rotated to 13 degrees - 15 degrees nose up body attitude at VR [in
the case of the FAR Part 25 airplane from whose flight manual this was
quoted], the airplane will attain V2 airspeed before a height of 35 feet
is attained [the First Segment 'screen height'].  This varies with weight,
altitude, temperature and [whether the aircraft's air condition packs are
ON or OFF]."

> One of the replies implied that it's decided by each airline
> individually--AA revised their manuals following the crash.  That
> doesn't seem right;  surely V2 isa property of the aircraft, and should
> not be left to each airline to determine.

Probably not so, per the above definition.  Where airline-to-airline
procedures *can* vary is, in the event of an engine failure, whether or
not an attained speed above V2 should be reduced back to V2.

In my own training by several airlines, the consensus seems to have been
to just "hold what you've got," rather than reduce.  This itself *may* be
a result of the Chicago DC-10 accident, but I have no way of knowing.

[Regarding the BirgenAir 757 crash ...]
> I don't know what spatial disorientation you're talking about, as no one
> else has mentioned it on this thread.

This accident happened at night, probably with no visible horizon.  The
aircraft *may* have departed controlled flight early in the stall (does
anyone know if the FDR data confirm or deny this?).  Whatever the case,
there is little question in my own mind that the pilots were, in fact,
"spatially disoriented."

> Of course the nut of the problem for Birgenair (pending the NTSB report ;-)
> is deciding which intstruments are right, and to what extent.

Again not trying to second-guess an unfinished report, but it *appears*
that the crew may have been aware of an airspeed discrepancy early in the
takeoff roll.  *If* so, they could have - and IMO *should* have - made an
uneventful abort at a speed *well* below V1.

I would be enormously surprised if their Minimum Equipment List permitted
a takeoff with such a problem in the airspeed indicating system (but
someone please correct me if this is not the case).

Mark E. Ingram

MarkT@Mo-Net.Com (also mingram@mail.orion.org)