DDM 30-03-03B 737NG

[RocknRola87]

Hi guys !
bullet number 5 in the DDM states :
Apply a fuel mileage decrement of 1.3%. to account for the engine and nose cowl anti-ice valve inoperative open.

how do you actually apply that on the OFP fuel figures. I have an idea but I’m not convinced, if someone can help. Thanks !

[FlightDetent]

Shooting in the dark, but one of the key parameters entering the fuel iterations of OFP is still-air-distance.

The quoted wording sounds like an invitation to apply factoring to that number?

[RocknRola87]

Yep, but it applies only to the trip, the thing it must be applied to all take off fuel components. The fuel mileage as you know is the specific range ( 1/distance consumption) expressed as nAm nautical AIR miles .I think the first step is to calculate fuel mileage = true airspeed / total fuel flow , then apply the 1.3% decrement & then recalculate the corresponding fuel flow resulting from that decrement. The final step is the take off fuel = the corrected fuel flow time the total time ( corresponding to T/O fuel on the OFP). But still inaccurate in my sense…wondering if there is a feature integrated in the OFP that makes the calculation upon an MEL input ?

[FlightDetent]

I see, stretching the SAD would extend the CRZ segment only and the added mileage would be compensated with CRZ Fuel Flow. Is there a chance that is what the MMEL wants you to do?

Not claiming this is the exact effect of the deviation, simply that this calulation provides fuel penalty sufficient to cover the added requirement of what is actually going on....

[RocknRola87]

Here is the rest of the operation text of the MEL :
30-03 Engine and Nose Cowl Anti-Ice Valves (Continued) 30-03-03B Valve Inoperative Open (Continued) OPERATIONS (O) (Continued)

4. During ground operations with the APU running, turn the engine bleed OFF whenever the associated engine is not running.

5. Apply a fuel mileage decrement of 1.3%. to account for the engine and nose cowl anti-ice valve inoperative open.

6. Apply the following additional fuel mileage decrement to account for flight in icing conditions which require a minimum of 60% N1 on the associated engine:

A. 2.0% for trip distances less than or equal to 1000 nautical miles.

B. 1.0% for trip distances greater than 1000 nautical miles.

7. All thrust rating limits except Takeoff and Go-Around, are reduced by 1.1% N1.

8. Enroute climb limited weight is reduced by 4,000 lb. (1,810 kg).

NOTE: Enroute climb penalties are based on single engine operating speeds that approximate maximum lift-to-drag ratio speed. To account for the difference in level off altitude when operating at other speeds, multiply the enroute climb weight penalty listed above by the appropriate factor listed in DDM Section 3, Enroute Diversion Speed Effects.

9. At temperatures greater than 50 degrees F (10 degrees C):

A. Takeoff and go-around thrust limits are reduced by 1.4% N1.

B. Takeoff and landing performance limited weights are reduced by 9,500 lb (4,309 kg).

10. For temperatures at or below 50 degrees F (10 degrees C), base performance limited weights on Engine Anti-Ice ON.

Sorry for the condensed text 😅