View Full Version : 737 Classic Rules of thumb.

24th May 2004, 01:56
Would any of the thousands of 737 pilots out there like to share their best rules of thumb concerning the 737-300 please.Especially climb descent profiles / fuel etc.

Young Paul
24th May 2004, 11:59
For fuel, add about 200-800 kg to the required fuel figure at the bottom of the nav log and round it up to the next hundred, to work out what to put in the tanks.

For descent, three miles per thousand feet works surprisingly well at almost all stages of the flight. Don't forget to allow a few miles for deceleration, and allow for the effect of wind.

24th May 2004, 15:16
10 knots reduction in V1 equates roughly to a decrease of 700 feet stopping distance.

At Vref minus five knots, ISA, sea level, flap 40 and 46,700 kgs the loss of lift due 5 knots (same incidence) is 7500 lbs. A two degree decrease of incidence at same IAS means 16,000 lbs loss of lift. A five degree Celsius increase in OAT will cause 3000lbs loss of lift..

Flap 30 in lieu of flap 40 from 1500 ft to touchdown saves 25kgs of fuel. 1600 kgs reduction in landing weight means trip fuel reduced by 3.5%

Info from various Boeing Airliner magazines over the years and applicable to the B737-200.

24th May 2004, 21:21
Rules of Thumb

A few handy rules of thumb for flying the 737-3/4/500.

Speed, Height, Distance conversion

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'

Approach Profile Planning

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

Aim for 210kts, On ILS at 12nm

Cruise N1

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


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

N1's & Pitch Attitudes

Phase of flight
Attitude (deg nose up)

Level Flight:



Flap 1, 190kts

Flap 5, 180kts
62 7

Gear down, flap 15, 150kts

Gear down, & on glideslope:

Flap 15, 150kts
Flap 25, 140kts

Flap 30, Vref + 5

Flap 40, Vref + 5

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.

Climb Speeds

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

Best Angle = V2 + 80

Best Rate = V2 + 120

Kinetic Heating

Is approximately 1/10kts IAS

Fuel Burn Vs Level

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

TFR = Weight reduction x Flight time in hrs x 3.5%

eg 60pax = 4200kg x 1hr x 3.5% = 147kg lower trip fuel

All taken from www.b737.org.uk/rulesofthumb.htm if anyone has any more let me know and I will add them to the list.

S & L

25th May 2004, 02:26
Engine Anti-ice burns 90 kg per hour.
Engine + Wing Anti-ice burns 250 kg per hour.

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.

Young Paul
25th May 2004, 20:21
Using 2 minute legs in the hold rather than 1 minute legs saves you 50 kg of fuel per hour.