Re: 727 cooper vanes

Date:         16 Sep 97 02:35:26 
From:         Richard Duncan <skylark@gte.net>
Organization: Skylark
References:   1 2 3 4 5
Next article
View raw article
  or MIME structure

Chris Dahler wrote:
> Steven McDowell wrote:
> > Chris Elberfeld wrote:
> > >
> > > A strong wind blowing in the right direction across the tarmac can
> > > deflect the Cooper switch, causing ramp wokers to have to jump
> > > up and down trying pull the switch back so the rear steps can
> > > be lowered.
> >
> > This doesn't sound too safe if these stairs are supposed to be available
> > as an emergency exit.
>
> Actually, the aft airstairs are not certified as a required emergency
> exit on the B727.  They are free to be used as a exit point during an
> emergency, but the airplane was certified without considering them
> available.  The reason is the stairs have no emergency way of getting
> them open if the fuselage is slightly twisted or comes to rest not up on
> the landing gear; when you release the uplocks, hydraulic pressure from
> the aircraft system helps to get the stairs down, but it is at a
> dramatically reduced pressure from the system.  In order to certify the
> stairs as an emergency exit, there would have to have been some sort of
> high-pressure gas or hydraulic charge to forcibly blow down the stairs
> in the event that normal hydraulic pressure didn't work.  I believe
> there were a few 727s ordered by TWA with such a system, but not many at
> all.

Except for the comment about the certification of the stairs I agree
with your comments.  On many 727-100's (the model without the pair of
LH/RH aft doors, and with oval number 2 inlet) Boeing and the airlines
certified the rear airstarirs as an emergency exit for high density
seating arrangements.  The Eastern (and Delta?) Shuttles used a number
of the airplanes so certified.  The system consisted of two self
contained actuators - one on each side of the stair located just above
the stair up latches.  When activated from either inside or outside of
the airplane these cylinders would extend - breaking the latch assembly
and pushing the stairs downward - If the airplane were sitting on it's
tail (ie main gear gone - with nose gear still extended) the system
would actually lift the tail of the airplane off the ground 18 to 20
inches and could hold it there for the time it takes to evacuate the
airplane.  During operation the plane would be supported on three points
- wing tip - nose and stairs.  This system effectively renders the DB
Cooper type device useless as the system can easily overpower the steel
vane mounted on the aft body/stair interface.  As a side note several
instances of inadvertant actuation of the system occurred at Piedmont,
and Eastern over the years, usually during ground servicing of the cabin
- the stairs would blow down so hard that substantial damage could occur
to both the stair and the airframe.

These comments are mine alone and not that of my employer - thanks

Richard Duncan