Re: DC-9 Flight Control

From:         Doug Snow <dougie@mama.indstate.edu>
Date:         21 May 96 11:10:50 
References:   1
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On 20 May 1996, billie durso wrote:

>     I am pretty sure that all of these earlier aircraft had mechanical
> linkages to all of the primary flight control surfaces.  I also am
> pretty sure that these mechanical linkages were hydraulically boosted
> to easy in control of the aircraft.  Assuming a total power failure in
> the aircraft, are these hydraulic boosters shutdown?  If so the flight
> surfaces would become excessively hard to control.  If anyone out there
> has any experience with the design of these aircraft please give me an
> answer about this.  Could a fire in the main fusebox cause a total
> power fialure throughout th e aircraft.?  Let me know.  Thanks
>

Speaking only about the B727, of which I have a flight manual (an old
piedmont manual), there is a method of control called manual reversion.

Manual reversion is where the trim tabs on the control surfaces fly the
surface into position responding to a control wheel deflection.  The
checklist to fly this procedure is very short:

"MANUAL FLIGHT CONTROL, LOSS OF HYD 'A' AND 'B'.

NOTE: Larger control forces and movements should be anticipated.  Observe
yaw damper limitations.  Avoid crosswind or turbulence.

SYSYEM A RUDDER HYD SWITCH - OFF (STANDBY RUDDER ON)

LANDING FLAPS - 15 (SEE ALTERNATE FLAP EXTENSION, PP. 1-307-8.)

BUG SPEED - VREF FOR 15 FLAPS.

GPWS INHIBIT SWITCH - INHIBIT (LOGBOOK WRITE-UP REQD)

ANTI-SKID - ON

NOTE: A full stop landing can be made easily with brake accumulator only.
Use steady brake pressure and hold.  Do not pump.  Use pneumatic brake
pressure as a last resort; see Pneumatic Brake Operation, p. 1-303-7.

In the systems description section, page 12-10-1

"With bost hydraulic systems unavailable, movement of the control wheel
moves the inboard aileron control tabs which 'fly' the inboard ailerons.
With flaps extended, movement of the inboard ailerons mechanically moves
the outboard ailerons."

hope this helps some

-----
Douglas Snow                                 dougie@mama.indstate.edu
                                http://mama.indstate.edu/users/dougie
Ex Northwest Arlns  ESE, MSP Ramp, Green Concourse
FAA PPL, IR, and ADX(in training)                   B727 Page Curator