who have been around the JT8 awhile would have heard about this already,
I'll just run through it for any new type people.
Over the years
there has been several reports of JT8's not responding to throttle movement,
(it's not widespread)
Your main fuel pump has two shafts the main one connects to the engine
gearbox and drives the fuel pump. The boost shaft (control shaft) connects
to the main fuel control and provides engine RPM (N2) information. Now
a failure is the main shaft is quite straightforward. It will cause a
complete loss of fuel flow to the engine resulting in it shutingdown.
A failure of the control shaft can cause one of the following conditions
If there is wear on the splines and ratcheting on the shaft this can cause
a partial loss of the N2 signal. The main fuel control will schedule fuel
flow at a higher than normal rate to compensate for this. N1, N2, EPR
and EGT will increase possibly past the red lines. It's normally of short
duration, but there's a good chance it will be followed up by the next
If there is a complete loss of the N2 signal the main fuel control will
revert to zero speed protection mode. It's designed this way so to ensure
high power and will not go to low power during critical phases of flight.
In this situation the main fuel control will command to a high power setting
(90% - 95% N2) for all operating conditions. During this mode the engine
will NOT respond to throttle movement. The only control you have is via
the engine start lever or pulling the fire switch.
There is a flight
operations technical bulletin on this recently which you may see in a
company form at some point. You should comply with whatever instructions
are received on the issue. The source document basically says to do the
Ground Operations: Failure to high power setting shut down malfunctioning
Take Off: If during the TO roll continue, climb to safe altitude,
stabilise the airplane and carry out the required check list. If an abort
is decided upon you will need to shut down the affected engine to maintain
directional control and stop the airplane.
Climb, Cruise,Decent,Landing: Maintain safe altitude stabilise
the airplane carry out required check list.
secret to this is to be aware of what's happening around you, It can happen
so don't just sit there, fat dumb and stupid or they will move you into
the training department.