Joined: 11 Dec 2005
|Posted: Thu Feb 07, 2008 4:52 am Post subject: B737-300 Maximum Altitude
|Maximum altitude is the highest altitude at which the airplane can be operated. It is determined by three basic characteristics, which are unique to each airplane model. The FMC predicted maximum altitude is the lowest of:
- Maximum Certified Altitude (structural) – Determined during certification and is usually set by the pressurization load limits on the fuselage.
- Thrust Limited Altitude – The altitude at which sufficient thrust is available to provide a specific minimum rate of climb. Depending on the thrust rating of engines it can be above or below the maneuver altitude capability.
- Buffet or Maneuver Limited Altitude – The altitude at which a specific maneuver margin exists prior to buffet onset. This altitude provides at least a 0.2g margin (33 degree bank) for FAA operations or a 0.3g margin (40 degree bank) for CAA / JAA operations prior to buffet.
To get the most accurate altitude limits from the FMC, ensure the following entries are accurate:
- Airplane weight
- Cruise CG
- Temperature deviation at the cruise altitude
The bank angle limiting function of FMC protects the commanded bank angle from exceeding the current available thrust limit. This function is only available when in LNAV. For operations other than LNAV, fly at least 10 knots above the lower amber band and use bank angle of 10 degree or less when operating at or near maximum altitude. If speed drops below the lower amber band, immediately increase speed by doing one or more of the following:
- Reducing angle of bank
- Increasing thrust up to maximum continuous
Flight above the maximum altitude is not recommended because:
- FMC fuel predictions are not available above the FMC maximum altitude.
- VNAV is not available above the FMC maximum altitude.
- Fuel burn increases at or above maximum altitude.