Re: landing flaps

From:         arch6@inlink.com (Archibald McKinlay)
Organization: McKinlay & Associates
Date:         30 Aug 95 14:12:51 
References:   1 2
Followups:    1
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In article <airliners.1995.1305@ohare.Chicago.COM>, jamest8469@aol.com
(JamesT8469) wrote:

> That is not the normal sequence for flaps and gear extension

This is due to the usual arrangement of the design in that the flaps do
usually have a higher design deployment speed.  In the case of certain
applications, maneuvering flaps for example, flaps have been made to
extend at relatively high, >300kts, speeds.  Landing gear has not been so
designed as there is little to be gained in designing a higher deployment
speed.


>However there is nothing wrong with doing this if you are in the airspeed
>limits for the flaps and gear extension.

Gear extension speeds are predominantly a function of the doors or other
fairing assemblies or lights.  Most tubing, such as hydraulic lines for
brakes and electrics for anti-skid, are tied down well enough they are not
a problem.  In the military we had several inadvertent deployments on
various jets and all that happened was usually door loss.  Some flail
injury to the tubing did occur but nothing to impair functionality.  If
other factors are involved, such as corrosion or an overserviced strut,
there can be more severe consequences.  These gear extension speeds are
ususally well above placard limits because they are worst case conditions,
not usually found in landing sequence.  BTW, one inadvertent extension was
at over 450kts in a dive bomb run....

Inadvertent flap deployment at high speeds can result in jammed flap
tracks and in some cases result in severed hydraulic lines or even loss of
a flap edge or wing overstress.  These are design and routing dependent
hazards.  The choices are often driven by design approach speed and
glideslope, space in the wing, fuel cell placement, drive mechanism size
and orientation, etc.  Speeds at which these occur usually are only a
little above placard limits because this worst case can occur in the
landing sequence.

> Perhaps the pilot was using the gear to more quickly slow the aircraft
> to the flap extend speed restriction. Sometimes the approach to LAX
> requires alternate techniques to meeting the situation at hand...

I also have had commercial reports of flaps and gear out of sequence
simply to adjust speed, funny that speed brakes are not there when you
need them....
This type of ad hoc checklist change has also resulted in gear up
approaches and some gear up passes.....

--
Truth arises from disagreement amongst friends, D. Hume (Scotland)
       eine Flucht nach Vorn machen, make a retreat forward
Loved and Missed, so Work Together and Rejoice, Phillipians 4:1-13
Archibald McKinlay, VI    Booz Allen & Hamilton/McKinlay & Associates
Software Safety Engineering and Management           arch6@inlink.com