Fuel System and Fuel Measurement - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 68

4.2.4 Notes on ETOPS and Additional Fuel
The National Aviation Authority may grant ETOPS approval to an airline operator
for certain twin engine jet aircrafts, provided that the operator complies with
special requirements in addition to the conventional flight conduct, including
enhanced reliability, maintenance and operation of the aircraft and training,
checking, licensing of its relevant flight crew and flight dispatch personnel, and the
procedures they must follow [ 36 ].
The time limits 90, 120, or 180 minutes are specified in the ETOPS Approval
defining the maximum distance that an aircraft can be further away from an
airport. The ETOPS flight planning rules require that the whole flight path be
covered by the circles drawn with ETOPS time limit radius around selected air-
ports [ 37 ].
Those airports must meet strict requirements also for in-flight emergencies and
contingencies such as engine failure or loss of cabin pressure and are called En-route
Alternate Airports (ERA).
Moreover, ETOPS flight planning involves mandatory critical fuel scenario
analysis for each ERA pairs and for each ERA of an ERA pair along the flight
path. The aim of this analysis is to ascertain that fuel actually remaining in the
tanks over a midpoint between two subsequent ERAs will be enough to reach
either of the two ERAs or the original destination airport. The midpoint between
two ERAs must be an Equal Time Point (ETP) [ 38 ].
That is, a point requiring equal flight time to reach any one of the two ERAs, i.e.,
the time to fly the distance corrected for wind effects. The analysis must consider
and compute the fuel amount required for cases when both engines operate, i.e.,
long-range cruise and when one engine is inoperative, i.e., cruise with selected
ETOPS speed. Over an ETP rapid decompression must be assumed with an
emergency descent to 10,000 ft (3,050 m), than cruising on 10,000 ft up to ERA.
Over the ERA a descent to 1,500 ft, i.e., 457 m and holding for 15 min follows,
then a missed approach is executed after which an approach and a successful
landing is made [ 39 ].
Other items in critical fuel analysis are considered for the required fuel amounts
are:
• Unreliable weather forecasts up to 5%;
• Expected Auxiliary Power Unit consumption up to 2%;
• Low temperatures or icing up to 1%;
• Engine degradation up to 5% [ 40 ].
Figure 4.8 presents a critical scenario with ETP conditions considering ERA1
and ERA2.
Except for extra fuel, none of the above-mentioned fuel items are allowed to be
used for purposes other than its specific role, i.e., to cover unexpected delays or
reroutes. So, any time when a flight on its way ought to deviate from its original
plans, a complete re-planning is mandatory. The re-plan shall ensure that the actual