APU Operations

[icefr8dawg]

XP via the checklist FOM limitations and transition in the early part of the flight

800A apu goes off during the line ups and valves come on right after takeoff. Now, if it's super, super hot I have knows pilots that'll takeoff with the main air valves open and have a hair trigger there to close them in the event... The Solar will run in flight but it's easier to explain the air valves on oops than a burping, smoke blowing, mis adjusted apu on takeoff.

 

[capt_zman]

Gear Up! has it right on. Also, I would never start the APU on descent because if something were to go wrong during the start (which happens quite frequently) it can take your attention away during a critical phase, as well as put alot of fire and hot air in the tail section during approach (apu fire on short final once, not fun).

You have plenty of time to start the APU on the ground after landing.

Also, another rule of thumb learned from experience is never leave the airplane with the APU air on. Sitting on the ramp one time, pop, pop, pop, I notice a bunch of breakers popping. Go outside and open up the hell hole and bang, a bleed air leak is basically melting the tail cone. I shutdown the APU before any real damage occurred. If I hadn't been there, it would have been a total loss of the airplane due to fire. Lesson learned.

 

[blzr]

Doi you wash your airplane? if so, turn the APU off below 4000msl, or the tail will turn black. Also, if you have the APU on, turn on the gen. That wat if you lose a generator on t/o, you will not load shead. Our APU doesn't pressurise the cabin as well as the engine bleads, so in flight, your ears pop a little faster. Use your own judgement when to turn it off.

 

[Gear Up!]

XP
Descending through 4000 FT
APU ON (Let spool up)
CABIN RATE SET TO ZERO
MAIN AIR VALVES CLOSE, (AT SAME TIME) APU BLEED AIR ON
(THIS TAKES CARE OF ANY CABIN DUMP)

 

[sleepy]

DA-900B and 50EX, APU approved for ground operation only. We start it 45 minutes prior to departure (start unloaded), usually shut it down on the after start checklist (shut it off loaded).

We start it again on the after landing checklist.

 

[Gulfstream 200]

I am looking for some advice on APU operation. I would like thoughts from Hawker and Non-Hawker Operators. Ours is available in flight, so here are the questions I have.

Start up and Shut down Altitudes?

Generator on or off?

Shut down Loaded? Gen, or Gen and Bleed?

Any other tips are welcome. Thanks

APU is shutdown after takeoff once main air valves are fully open
APU is started around 10 minutes out on descent

Generator is off for takeoff (tripped before bus tie check and stays tripped)
Generator is on for landing

Shutdown loaded, GEN & Bleed.

 

[400A]

APU is shutdown after takeoff once main air valves are fully open
APU is started around 10 minutes out on descent

Generator is off for takeoff (tripped before bus tie check and stays tripped)
Generator is on for landing

Shutdown loaded, GEN & Bleed.

For Hawker specifics, There was a debate during school, and I am still leaning away from shutdown with the bleed on, because if you get a bleed valve fail light during the shut down it was my understanding from school that you could not leave the main air valves on with that valve stuck open and therefore now you are committed to unpressurized flight. If the Valve was stuck open then you could at least continue below 30,000 ft pressurizing with the APU. Thus I always make sure to close the valve and make sure it closed before killing the APU. As you know, this is not covered in the checklist. I do not have the APU section of the AFM here at the house. Did I Misunderstand something? Back to back initials is enough to confuse anyone.

 

[G100driver]

I love those school debates. It got so bad on Falcon 2000 that Honeywell sent out a letter telling everyone not to mess with it.

Just push the grren button and let ECU do the rest.

 

[400A]

I love those school debates. It got so bad on Falcon 2000 that Honeywell sent out a letter telling everyone not to mess with it.

Just push the grren button and let ECU do the rest.

No Green Button on the Hawker. Not that simple in my opinion.

 

[fu69atacafyeah]

For Hawker specifics, There was a debate during school, and I am still leaning away from shutdown with the bleed on, because if you get a bleed valve fail light during the shut down it was my understanding from school that you could not leave the main air valves on with that valve stuck open and therefore now you are committed to unpressurized flight. If the Valve was stuck open then you could at least continue below 30,000 ft pressurizing with the APU. Thus I always make sure to close the valve and make sure it closed before killing the APU. As you know, this is not covered in the checklist. I do not have the APU section of the AFM here at the house. Did I Misunderstand something? Back to back initials is enough to confuse anyone.

If you get the APU bleed valve fail light DURING APU ops you're not supposed to open the main air valves. This is because you dont know the position of the APU bleed valve (could be open, closed, or partially open) which could cause damage...same reason why there is the 1 minute limitation of having the main air valves open and the APU bleed on.

When you shut it down loaded you'll get the bleed valve fail light, but because it's not running anymore producing air, you wont cause any damage. Then when you go to start it on the other end of the flight you will be good to go because you will have turned the APU master off, then on, the APU GEN switch off, and the APU bleed switch off.

I think the AFM recommends it to be shut down loaded but I dont have it with me.