Crash re-engagement
#1
Gets Weekends Off
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Joined APC: May 2017
Posts: 258
Crash re-engagement
What exactly is it? According to a 767 sim checkride prep manual I read it doesn't exactly saw what it is but that it is caused by having pneumatic air being supplied to the plane while closing the shutoff lever. The manual says
IF YOU STILL HAVE ANY PNEUMATIC AIR SUPPLIED TO THE AIRPLANE
IN ANY WAY, THE STARTER WILL SLAM "ENGAGED" AT HIGH RPM...
ALL PNEU AIR MUST BE REMOVED BEFORE
THE START LEVER MOVED TO CUTOFF !!
If you mistakenly do
the immediate action step for abnormal start and shut off the start lever …
YOU WILL HAVE A POSSIBLE CRASH RE-ENGAGEMENT!!
IN ANY WAY, THE STARTER WILL SLAM "ENGAGED" AT HIGH RPM...
ALL PNEU AIR MUST BE REMOVED BEFORE
THE START LEVER MOVED TO CUTOFF !!
If you mistakenly do
the immediate action step for abnormal start and shut off the start lever …
YOU WILL HAVE A POSSIBLE CRASH RE-ENGAGEMENT!!
#2
It means the starter tries to engage while the engine and N2 gearbox are already turning. Likely to break the starter and if you're really unlucky the gearbox.
Kind of like trying to start your car when the motor's already running (old cars would let you do that).
Kind of like trying to start your car when the motor's already running (old cars would let you do that).
#4
If the gearbox got damaged, that would be much more involved. All the accessories would have to come off, and then the gearbox.
If the damage included anything on the N2 spool, that might be an overhaul.
#5
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,021
Have you ever flown a light airplane with a manual landing gear extension that uses a crank? If so, were you warned not to let go of the crank while extending the gear, because the gear would freefall, and the spinning crank might break your fingers? That's crash engagement.
Ever try to shift gears on a manual vehicle without using the clutch? That's crash engagement.
To engage the starter, depending on the type of starter, the starter shaft must inserted into a splined drive on the engine (or in certain cases, an electromagnetic clutch engaged, much like an air conditioning compressor). If the engine is already turning too quickly, the starter shaft or shear coupling in the drive assembly can fail, or worse.
If this occurs in flight, it may negate the possibility of any attempts to perform a starter-assisted relight. It may also mean that the starter becomes engaged and stuck in that position, which means that if the engine is windmilled or run to a position higher than the starter limit, the starter can destruct. Whereas a generator will run on a constant speed unit (automatic transmission, governed to a particular speed), the starter motor is not; a stuck starter can burst or fail, which can lead to a number of subsequent failures, and catastrophic damage.
Ever try to shift gears on a manual vehicle without using the clutch? That's crash engagement.
To engage the starter, depending on the type of starter, the starter shaft must inserted into a splined drive on the engine (or in certain cases, an electromagnetic clutch engaged, much like an air conditioning compressor). If the engine is already turning too quickly, the starter shaft or shear coupling in the drive assembly can fail, or worse.
If this occurs in flight, it may negate the possibility of any attempts to perform a starter-assisted relight. It may also mean that the starter becomes engaged and stuck in that position, which means that if the engine is windmilled or run to a position higher than the starter limit, the starter can destruct. Whereas a generator will run on a constant speed unit (automatic transmission, governed to a particular speed), the starter motor is not; a stuck starter can burst or fail, which can lead to a number of subsequent failures, and catastrophic damage.
#6
Have you ever flown a light airplane with a manual landing gear extension that uses a crank? If so, were you warned not to let go of the crank while extending the gear, because the gear would freefall, and the spinning crank might break your fingers? That's crash engagement.
Your other examples are valid.
#7
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,021
Not really. The gearing and manual extension handle are already engaged when you begin the extension process. What you describe is just an uncontrolled extension due to the air load on the gear as it extends (spinning the crank dangerously).
Your other examples are valid.
Your other examples are valid.
The crash engagement is the fingers and the handle, once the handle is already spinning.
Hence the broken fingers.
Perhaps you've never experienced that in a light twin...same principle, but in this case, the pilot's hand is the one crash engaging.
All the examples are valid.
#8
You missed the point.
The crash engagement is the fingers and the handle, once the handle is already spinning.
Hence the broken fingers.
Perhaps you've never experienced that in a light twin...same principle, but in this case, the pilot's hand is the one crash engaging.
All the examples are valid.
The crash engagement is the fingers and the handle, once the handle is already spinning.
Hence the broken fingers.
Perhaps you've never experienced that in a light twin...same principle, but in this case, the pilot's hand is the one crash engaging.
All the examples are valid.
#10
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,021
In the case of dusted knuckles with the gear, I'm the idiot that let go...
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