The minimum fuel that a commercial flight must uplift is defined in the regulations, ICAO Annex-6. The fuel required is what is expected to be used from departure to destination, if unable to land then fly the missed approach procedure and then fly to the alternate. When the aircraft reaches the alternate airport, the aircraft needs fuel to hold over the alternate for at least 30 minutes before commencing the approach to land.
While most airlines uplift minimum fuel as per regulatory requirements, there are a few airlines which depend on statistical analysis and have a pragmatic approach to the fuel requirement. One such airline that I flew with was IndiGo, in India. The flight operation setup was established and managed by a seasoned aviation professional. While airlines, in general, do not quantify the cost of a diversion because they are not able to assign a value to the intangible cost, IndiGo worked on a fixed percentage of diversions which were acceptable.
As per ICAO, where a destination alternate aerodrome is required, the amount of fuel required to enable the aeroplane to:
i) perform a missed approach at the destination aerodrome;
ii) climb to the expected cruising altitude;
iii) fly the expected routing;
iv) descend to the point where the expected approach is initiated; and
v) conduct the approach and landing at the destination alternate aerodrome
It all seems safe and logical. Have you ever wondered what this missed approach is? How much fuel is required for the missed approach segment? Do the airlines carry enough fuel for this segment, especially when it is long?
A missed approach procedure is the procedure to be followed if an approach cannot be continued. It specifies a point where the missed approach begins, and a point or an altitude/height where it ends. A missed approach procedure is specified for all airfield and runway Precision Approach and Non-Precision Approach procedures. The missed approach procedure takes into account de-confliction from ground obstacles and from other air traffic flying instrument procedures in the airfield vicinity. Only one missed approach procedure is established for each instrument approach procedure.
If the flight planning software misses out on this important segment, then at some places on the globe, there will be a significant difference in the fuel required v/s actual uplift. The above missed approach procedure is an example of a long procedure which would required significant fuel to be uplifted as per regulations.
The above procedure is between 70-90 nautical miles long. A mid-size jet would require approximately 600-700kgs of fuel if required to fly the complete procedure before being able to set course for the alternate airport.
There is a need for the airlines to ensure that the fuel uplift for the flight includes the realistic missed approach procedure fuel and that the aircraft would fly if unable to land at the destination. With the growing complexity of the airspace,this becomes a safety issue for airports as the ones mentioned above where the missed approach procedure is longer than the usual segments.