757 Aircon pack control

[it will do the trip]

A couple of flight deck procedure questions as I'm an oily engineer on a 757 course at mo and hopefully a few answers will help to explain all the different pack control modes.

1. What is the procedure for a 'ZONE' inop warning on the temp selectors?
2. Under what circumstance would you revert to using STBY pack control? which mode do you use N,C,W? and what do you notice as the difference between each?
3. Do you ever turn trim air off? Does trim air work in STBY?

Thanks in advance.

[mondriver]

Evening !

Your points:

1. ZONE INOP on a zone temperature is not a big issue. The temp controller switch would just be placed off, and that zone would uncontrolled as far as temperature is concerned. If all 3 zones were INOP, a constant 24c would be produced for all zones....(same as turning the trim air switch off !)

2. STBY pack control is used with a fault with the auto-temperature controller. PACK INOP is the EICAS message...which could be either....a)fault in auto temp controller OR Excessive Pack OUTLET temperature. STBY N,C,W is used to regulate a crude mean temperature of air to the cabin...namely 75,65 and 85 degrees respectively.

3. No..you don't turn trim air off, and YES it works in STBY (assuming you still have trim air switch turned on), as trim air warms the cabin to the temp set on the stby switch....65,75,or 85 degrees. The packs satisfy the compartment with the coolest demand, and trim air warms the other two zones.

Hope this answers your q's !

Cheers

Mon

[neil_further]

The main thing to know as an engineer is where to hit it when the pack doesn't start, they are prone to sticking on the air bearings.

[M.Mouse]

3. No..you don't turn trim air off

Sometimes you do.

QRH procedure for either Flight Deck, Forward Cabin or Aft Cabin Temperature controller inop. states that if the affected temperature continues to be to warm or too cold with the affected compartment temperature controller turned off then:

Trim Air.........Off

From my experience just last week it is sometimes necessary.