The EDTO approval process for large aeroplanes is valid for regular public transport (RPT) or charter operations which include certain cargo operations. To be eligible for EDTO, the specified airframe/engine combination must have been certificated to the airworthiness standards of Transport Category aeroplanes Federal Aviation Regulation (FAR) Part 25, the European Aviation Safety Agency (EASA) CS25 or the equivalent.
Three levels of operational approval are used for two- engine aeroplanes:
- EDTOs with a maximum diversion time from 90 minutes up to 180 minutes to an en-route alternate (at the approved one-engine-inoperative cruise speed under standard conditions in still air);
- EDTOs with a maximum diversion time from 180 minutes up to 240 minutes to an en-route alternate (at the approved one-engine-inoperative cruise speed under standard conditions in still air); and
- EDTOs with a maximum diversion time above 240 minutes (at the approved one-engine-inoperative cruise speed under standard conditions in still air).
In the case of aeroplanes with more than two engines level of approval is used, above 180 minutes (at the approved one-engine inoperative cruise speed under standard conditions in still air).
Note: In the case of all EDTO beyond 180 minutes, additional flight dispatch requirements apply.
System redundancy levels appropriate to EDTOs must be reflected in the Master Minimum Equipment List (MMEL). An operator's MEL may be more restrictive than the MMEL considering the kind of EDTO proposed and equipment and service problems unique to the operator.
EDTO alternates serve a different purpose than the destination alternate aerodrome, and would normally be used only in the event of an engine failure or some other aeroplane system failure, an aerodrome must not be listed as an EDTO alternate unless the requirements are met.
The procedures established by the operator must ensure that EDTO is limited to flight plan routes where the approved maximum diversion time to EDTO alternates can be met under standard conditions in still air. Operators must provide for:
- Company procedures to state that, upon occurrence of an in-flight shut down of an engine in a two-engine aeroplane, the pilot must promptly initiate diversion to fly to, and land at, the nearest aerodrome, in terms of time, determined to be suitable by the flight crew; and
- A practice to be established such that, in the event of a single or multiple EDTO Maintenance significant system failure, the pilot will initiate the diversion procedure to fly to, and land at, the nearest aerodrome in terms of time, determined to be suitable by the flight crew, unless it has been justified that no substantial degradation of safety results from continuation of the planned flight.