From: ritter@claude.ma30.bull.com (Roger Ritter)
Newsgroups: rec.aviation
Subject: Air restart of jets (long)
Date: 10 Sep 92 14:05:29 GMT
Organization: Bull HN Informations Systems Inc.

Recently, someone posted asking about air restart procedures for jet
engines.  I haven't seen any other posts, so I figured I'd dig out
some information for the public elucidation.  

Aerial restart on a jet is something that is different for each
aircraft.  The following are the procedures for two USAF jet trainers:
the T-37 and T-38.  The information is taken directly from the emergency
procedures sections of the flight manuals (T.O. 1T-37B-1, 1 Jan 1972;
and T.O. 1T-38A-1, 1 Jan 1972).  The information is old, but the
airplanes are still flying; I don't think this is terribly out of
date.  Headings done in all-caps are boldface in the manual; the
same holds for procedure steps.  A boldface procedure step is one
the pilot should memorize, since there won't be time to look it
up if you think you need it.

For the T-37:
ENGINE RESTART DURING FLIGHT
All airstart attempts should be made at an altitude of 20,000 feet or
below.

CAUTION

Prior to attempting an airstart, observe tachometer for engine windmilling.
If there is no indication of windmilling, the engine may have seized
and no attempt should be made to restart until a windmilling indication
is noted.

1.  Throttle (Dead Engine) - CUT-OFF

Note:  Use instructor's throttles when attempting a restart in order to
have cut-off features available.

2.  Fuel shutoff T-handle - PUSH ON.
3.  Fuel system - EMERGENCY.
4.  Fuel boost pump - ON.
5.  Inverter - MAIN or SPARE.
6.  Battery - ON.
6A. Circuit breakers - CHECK IN.
7.  Cockpit air - VENT.
8.  Starter and ignition - GND - ON and hold simultaneously.  If rpm is
       above 30%, allow the engine to windmill below 30% before attempting
       restart.
9.  Throttle - IDLE.

Note:  If flame out resulted from throttle linkage slip, it may be
necessary to advance the throttle beyond idle to effect a restart.
A start may not occur immediately.  RPM may drop as low as 12% before
signs of a start are observed.

10. Exhaust gas temperature - MONITOR.
       The first indication of a start is a rise in the exhaust gas
       temperature.
11. Starter and ignition - Release at 30% rpm.
12. Engine instruments - CHECK.

If starting attempt was unsuccessful:

13. Electrical load - REDUCE.
14. Attempt another start if warranted.


ENGINE RESTART - LOW ALTITUDE

If sufficient time is not available to accomplish the procedures
described in Engine Restart During Flight, the following procedure
should be used:

1.  STARTER - AIR POSITION, 16% RPM OR ABOVE.
2.  FUEL SYSTEM - EMERGENCY.  Leave fuel system in emergency for
         remainder of flight.

If rpm drops below 16%:

3.  STARTER AND IGNITION - GND - ON AND HOLD UNTIL 30% RPM.

WARNING

Throttle(s) must be in the operating range to accomplish an airstart.


From the T-38 manual:

RESTART DURING FLIGHT
Airstarts can be expected at or below 26,000 feet between 250 KIAS
and 310 KIAS.  Optimum restart capability at higher altitudes occurs
at 270 KIAS.  At lower altitudes, an engine RPM of 16% or greater 
affords sufficient airflow for restart.  If engine flameout is
experienced, use the following procedure:

1.  Altitude - 26,000 feet or below.
2.  Airspeed - 250 KIAS to 310 KIAS.

Note:  When the rear cockpit is occupied, the fuel pump circuit
breakers should be checked in.

3.  Battery Switch - Check ON.
4.  Boost Pump Switches - Check ON.
5.  Engine Start Button - Push Momentarily.
6.  Throttle (windmilling engine) - Advance to slightly above IDLE,
       then retard to IDLE.

Note:  Leave throttle at IDLE for 30 seconds before aborting a start.
If dual engine flameout occurs, right engine should be attempted first
as right engine instruments will operate normally as soon as engine
start button is pushed.

7.  If Restart Attempt Fails - Place throttle in OFF position for
       approximately 10 seconds, turn crossfeed switch ON, check
       engine start and ignition circuit breakers, and attempt
       another start.

Note:  The RPM may hang up during restart after combustion occurs
at low airspeeds.  RPM hangup during an airstart may be eliminated
by increasing airspeed.
If it appears that a boost pump has failed, remain below 25,000 feet.
Turn crossfeed OFF to avoid having to use an abnormal fuel balancing
procedure.
If it appears that a boost pump has failed and flight below 25,000
feet is impractical, engine operation above 25,000 feet with gravity
fuel flow is possible at reduced power settings.  If a reduced power
setting is also impractical, use crossfeed operation to insure boost
pump pressure and minimize the possibility of fuel flow interruption.
Monitor the fuel balance and descend as soon as practical.  Flight at
lowest practical altitude and reduced power settings will minimize
probability of fuel flow interruption.

ALTERNATE AIRSTART

The alternate airstart is primarily designed for use at low altitude
when thrust requirements are critical.  An airstart may be accomplished
by advancing the throttle to MAX range.  This energizes normal and
afterburner ignition for approximately 30 seconds (if throttle remains
in MAX range).  If the engine does not start after 30 seconds,
additional starts may be attempted by retarding the throttle out of
MAX range to reset the circuit and again advancing the throttle into
MAX range to reactivate the ignition cycle.  After engine start, the
throttle may be left in MAX range if afterburner operation is desired.

If alternate airstart is required, proceed as follows:

1.  THROTTLES - MAX.

WARNING

If throttle is already in MAX, recycle throttle MIL to MAX.
With dual engine failure, battery switch must be ON to provide ignition.

Note:  If the throttle is in the MAX range, pushing the start button
will also provide ignition; however, only for that period of time
which the button is held.



Well, that's the story.  Your procedures will be different.  I hope those
of you who were USAF pilots in the last 30 years or so enjoyed this
short trip down memory lane.

-- 
Roger Ritter N1FZZ (R.Ritter@ma30.bull.com) PP-ASEL, AGI
1946 Luscombe 8A N71983 "Rocky"
Sheep do not so much fly as plummet!        NH CAP: Profile 49