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Aircraft Flight Planning Topic 10.

Acceleration Calculations


Often due to a late departure, the crew have to try and make up time to arrive at that destination on time, and thereby not effect the departure time of a connecting flight. This will involve entering the altitude capability tables on page 2-14 of the B727 manual, so as to find the maximum aircraft gross weight (GW) at the planned flight level at which the aircraft can accelerate to the new, higher speed. In doing so we will ensure that maximum cruise thrust limits are NOT exceeded, which is extremely important as regards engine life.

Point to note:
  • Cruise mach number becomes more limiting the higher the aircraft flies, and the warmer the temperature.

Example 1. A B727 is flying from Perth to Adelaide on ERC H2 route Y19. It’s departure was delayed due to other traffic, and the crew attempt to make up some time.

Planned cruise schedule is Mach 0.80/FL330.

After take off the aircraft reaches TopC (FL330) at report point “HALIT” (150 nm from Perth) at 1500 UTC.

Conditions at 1500 UTC/FL330 are:

Spot wind 50 kt TAIL/ISA +10C. Aircraft GW at “HALIT” is 77, 500 kg.

Assuming the conditions and planned speed schedule remain unchanged, at what distance past “HALIT” can the aircraft be accelerated directly to cruise at M 0.82, without exceeding the engine max cruise thrust limits?

Step 1. Refer to manual page 2-14 to find that heaviest weight at which the aircraft can accelerate directly from Mach 0.80 to M 0.82 in ISA +10 conditions at FL330 is 75, 100 kg. This means we will have to maintain M 0.80 until the aircraft GW has reduced to 75, 100 kg. Fuel burn off (FBO) required is therefore 2, 400 kg (ie: current GW of 77, 500 kg - 75, 100 kg). The EMZW is half way between these weights at 76, 300 kg (say 76 Tonne).

Step 2. Fill in tAhe data box with TAS, groundspeed, fuel flow etc, and find the specific ground range (SGR).

Step 3. Divide the FBO required by the SGR to get distance to the acceleration point.

In this case 2, 400 kg divided by 8.71 kg/gnm = 275 gnm past HALIT. Answer !

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Marty says ... "Goodbye to GA".

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