Rules of Thumb

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Contents

Contents

• Speed, Height, Distance conversion

• Approach Profile Planning

• Cruise N1

• N1's & Pitch Attitudes

• Climb Speeds

• Kinetic Heating

• Driftdown

Fuel Consumption Formulae:

• Optimum FL

• Step climb & wind/altitude trade

• Trip Fuel Reduction

• Anti Ice

• Non-Normal Configurations

All of the information, photographs & schematics from this website and much more is now available in a 374 page printed book or in electronic format.

*** Updated 05 Aug 2023 ***

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Level flight deceleration allow 10kts/nm & 1kt/sec (deceleration is faster at lower weights)

Descending deceleration allow 5kts/nm & 0.5kt/sec

Idle descent allow 3nm/1000'

Aim for 250kts, 10,000ft by 30nm out

Aim for 210kts, On ILS at 12nm

N1 = (2 x Alt/1000) + 10   eg at FL350 = 70+10 = 80% N1

or

FF = (IAS*10)/2 -200  eg 250kts = 2500/2 -200 = 1050 kg/hr/engine

All the above based on a gross weight of 47.5, N1 may vary by 5% and attitude by 2° at other weights.

Add 2% N1 in turns.

For single engine add 15% N1 + 5% N1 in turns.

If ECON info not available, use 250KIAS until 10,000ft then 280KIAS/M0.74 thereafter.

Best Angle = V2 + 80

Best Rate = V2 + 120

Increases TAT by approximately 1°/10kts IAS

Driftdown

Driftdown speed and level off altitude are for the terrain critical case; if terrain is not critical you may accelerate to Long Range Cruise (LRC), this will cost approximately 3000ft. Otherwise slowly accelerate to LRC at the level off altitude as weight reduces with fuel burn. If anti ice is required, the altitude penalties are severe. See table below for figures (QRH PI.13.7).

Optimum FL   (FPPM p2.1.1)

Step climb & wind/altitude trade    (FPPM p3.2.16)

The 737 burns approx 30kg/min. Hence subtract (30kg x reduced trip time in mins) from the trip fuel at the proposed level. If this figure is less than the trip fuel for the planned flight level, the lower level is justified.

Trip Fuel Reduction = Weight reduction x Flight time in hrs x 3.5%

Eg: 10 pax less over a 2hr flight = 1000kg x 2 x 3.5% = 70kg lower trip fuel.

Landing Flaps

Flap 30 uses 25kgs less fuel than flap 40 from 1500 ft to touchdown.

Anti Ice

Engine Anti-ice burns 90 kg per hour.

Engine + Wing Anti-ice burns 250 kg per hour.

Non-Normal Configurations

Compared to 2 Engine LRC at Optimum Altitude for any given weight:

Engine Out LRC burns 21% more fuel.

Engine Out LRC increases Time Interval by 13%.

Depressurised LRC (2 Engines@10,000') burns 49% more fuel.

Depressurised LRC increases Time Interval by 20%.

Gear Down burns 89% more fuel! Gear Down increases Time Interval by 29%.

Hint. you can check the Depressurised figures quoted above by entering 10,000' as a "step altitude" in the CRZ page and compare the fuel remaining at your destination.