Re: SR111: Reality check please

Date:         13 Oct 98 02:48:20 
From:         TJH <n2ste@juno.com>
Organization: People for the Ethical Treatment of Mythical Animals
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.

6000+ initially, settling down to stabilize at approx 3500-4500fpm at Vmo(do
not exceed speed, barber pole), clean(no gear or flaps out)(B757 numbers)

> 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 ?

The aircraft would need to be stabilized at really no more than 250 knots to
allow for landing gear and flap extension by 15 miles out from the end of
the runway.  The more speed the airplane has the harder it will be to
touchdown ON the intended point of contact.  For every knot over planned
touchdown speed the aircraft will travel an additional  xxxx feet down the
runway to run off at the end.(I'm not in calculator mode and dont recall the
exact number)  I do remember seeing it in a post a few days ago.  Too much
speed and the aircraft floats down the runway still decelerating, but still
flying...

> 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).

Normal Vmo(do not exceed speed) varies from 350knots at sea level to about
280kts at altitude(37,0000-39,000-41,000').  In a slow speed descent, the
airspeed would be approx. 250kts and yield a descent rate of approx. 3,000
fpm.  When would you use the low speed over the high speed descent?  If you
have a problem in that  you suspect structural damage(collision, explosion,
flight control malfunction) or have a vibration that increases with an
increase in airspeed.  Otherwise, in  the case of a rapid decompression(loss
of cabin pressure) you would do a high speed descent to get back down to a
breathable altitude(10,000-12,000') as quickly as possible.(B757 numbers)

TJH, B757 IP
PHX.AZ