Design requirements. Type-design changes made in Parts 21, 25, and 33 of the U.S. federal aviation regulations codify existing ETOPS policies, practices, and special conditions in a uniform set of regulations for airplanes and engines. The new regulations also extend the existing safety standards to allow for design approvals beyond the previous 180-minute ETOPS diversion authority limit. These extended standards ensure that airplane designs approved for beyond-180-minute ETOPS maintain the same high standards that have exemplified ETOPS experience to date. As the FAA noted in this new rule's preamble:
"Because of the potential benefits associated with the superior design of airplane-engine combinations demonstrated under the existing [twinjet] ETOPS certification programs, the FAA has decided to extend those requirements to the airplanes with more than two engines should the manufacturer wish to market these airplanes as suitable for ETOPS operation."2
Boeing plans to certify the long-range versions of the 787 Dreamliner to allow operations up to its design capability. Boeing also plans to extend the diversion capabilities of certain models of the 777, and is looking into extending the cargo fire suppression capabilities of its three- and four-engine models like the new 747-8. These product decisions will be based on customer needs.
At present, it appears that a diversion time limit in the neighborhood of 330 minutes will support optimal flight operations between any two points on earth. Boeing is currently assessing the ability of our current and projected widebody fleet to meet this goal, and will in the very near future define program goals.
Dispatch. Revised regulation 14 CFR 121.631 makes only minor changes to the established ETOPS dispatch and flight-release requirements, which specify requirements for weather conditions at ETOPS alternate airports and require that weather information be updated at the start of the ETOPS phase of flight to verify the continuing availability of diversion airports.
Fuel reserve. New regulation 14 CFR 121.646 requires that all airplanes flown in extended operations must carry an ETOPS fuel reserve sufficient to allow flight to an ETOPS alternate airport in the event of these three scenarios:
- A rapid loss of cabin pressure at the most critical point followed by a descent to a safe altitude as defined by oxygen availability.
- A rapid loss of cabin pressure and a simultaneous engine failure at the most critical point followed by a descent to a safe altitude as defined by oxygen availability.
- An engine failure at the most critical point and descent to one-engine-inoperative cruise altitude and diversion at one-engine-inoperative cruise speed.
Whichever of the above requires the greatest amount of fuel shall be the basis of computation for this reserve. Because of the increased fuel consumption of turbine engines at low altitudes, and the corresponding reduction in airplane range, the decompression scenarios logically define this reserve, which ensures sufficient fuel for an extended low-altitude diversion followed by a descent to 1,500 feet at the alternate airport, a 15-minute hold, and an approach and landing. Further allowance is made for possible airframe icing, wind forecasting error, and in-flight use of the auxiliary power unit.
More than two decades of ETOPS twinjet experience have identified areas of excessive conservatism in the original ETOPS fuel reserve requirement. Based on the refinement of models and removal of past uncertainties, this new rule specifies a slightly smaller critical fuel reserve for twinjets. Under the new ETOPS rule, three- and four-engine passenger airplanes flying extended routes will be required to carry an ETOPS fuel reserve.
The FAA has also implemented a non-ETOPS provision, 14 CFR 121.646(a), that addresses an existing concern. This provision requires that all three- and four-engine airplanes carry a decompression fuel reserve whenever they fly beyond 90 minutes of an airport. Although U.S. regulations specify supplemental oxygen in the event that cabin pressure is lost, some operators and flight-plan suppliers have not specified sufficient reserve fuel for the airplane to reach an alternate airport during a low-altitude diversion. It should be noted that many three- and four-engine operators do routinely carry a depressurization fuel reserve as a matter of internal airline policy.