Derated thrust settings

[brent p h]

When is it practical to use clb-1, clb2, does this reflect how the aircraft is loaded? Or is it to satisfy noise abatement protocols? (Generally asking in regard to 737 or mainly Boeing aircraft)

[B767Driver]

Originally Posted by brent p h

When is it practical to use clb-1, clb2, does this reflect how the aircraft is loaded? Or is it to satisfy noise abatement protocols? (Generally asking in regard to 737 or mainly Boeing aircraft)

Under normal situations, my company does not use derated power settings. They actually burn more gas and cause more noise close in to the airport surroundings. In order to minimize noise, the best remedy is to achieve the most altitude in as little distance as possible...as the decibel level decreases exponentially with the altitude achieved.

We do use something called, the Assumed Temp Method, which is not a "derated" thrust setting, but a thrust setting based upon a maximum OAT.

In rare instances, where the ATM method won't achieve enough thrust reduction because so much excess thrust is still available (possibly the airplane is very light) then a derate clb-1 or 2 can be selected.

(Essentially a derate occurs at the fuel control unit but the Assumed Temp Method does not...the engine thinks it's a full power takeoff.)