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Extended Range Twin Engine Operation
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Extended range operations by aircraft with two turbine power units (ETOPS or EROPS) are sometimes necessary to permit twin engine aircraft to operate over very long sectors where the range from a suitable alternate aerodrome will exceed the maximum laid down in regulations. This maximum is laid down by national authorities and is normally the distance corresponding to 60 minutes flight time at the single engine cruise speed.
In this context, a suitable alternate aerodrome may be defined as one that has runways of sufficient length and strength to permit safe landing; possesses all the appropriate ancillary services (lighting, communications, emergency services, weather reporting, navigation facilities etc.) to permit a safe approach and landing; will be open for a period which covers the range of possible times of arrival; and which is forecast to have weather suitable to permit a landing throughout that period.
The diagram below illustrates the procedure. The operator wishes to fly from A to C. There is one suitable alternate airfield: B. The maximum range from an alternate normally permitted by national regulations is indicated by the red lines, therefore the flight is not permissible. The operator obtains ETOPS authorisation and the green lines show the maximum range from an alternate now permitted. The flight may now proceed to destination following route A - X - C, which involves only a small deviation from the direct route.
These provisions are used principally for fan-jet operations; however, ETOPS approval has been granted on at least one occasion for turbo-prop operations. The definition of ETOPS used by UK CAA (and perhaps other national authorities) extends these provisions to aircraft with reciprocating engines; however, it is doubtful if such aircraft could meet the demanding reliability requirements.
Approval to carry out ETOPS may be granted by national authorities subject to them being satisfied that the aircraft (including engines) meet certain standards of reliability,; that the operator has established appropriate procedures to support ETOPS; and that flight crews and operations staff are suitably trained in ETOPS procedures. ETOPS approval must be specified in the operator's Air Operator Certificate (AOC).
Extended range operations by aircraft with two turbine power units (ETOPS or EROPS) are flights where the flight time at the one power-unit inoperative cruise speed (in ISA and still air conditions), from a point on the route to an adequate alternate aerodrome, is greater than the threshold time approved by the State of the Operator. (ICAO Vocabulary).
Unless the operation has been specifically approved by the State of the Operator, an aeroplane with two turbine power-units shall not, except as provided [below], be operated on a route where the flight time at single engine cruise speed to an adequate en-route alternate aerodrome exceeds a threshold time established for such operations by that State. (ICAO Annex 6: Operation of Aircraft, Chapter 4, Para 4.7.1)
In approving the operation, the State of the Operator shall ensure that:
- a) the airworthiness certification of the aeroplane type;
- b) the reliability of the propulsion system; and
- c) the operator’s maintenance procedures, operating practices, flight dispatch procedures and crew training programmes;
provide the overall level of safety intended ... . In making this assessment, account shall be taken of the route to be flown, the anticipated operating conditions and the location of adequate alternate aerodromes. (ICAO Annex 6: Operation of Aircraft, Chapter 4, Para 4.7.2)
A flight to be conducted in accordance with [ETOPS procedures] shall not be commenced unless, during the possible period of arrival, the required alternate aerodrome(s) will be available and the available information indicates that conditions at those aerodromes will be at or above the aerodrome operating minima approved for the operation. (ICAO Annex 6: Operation of Aircraft, Chapter 4, Para 4.7.3)
In order to maintain the required level of safety on routes where an aeroplane with two power-units is permitted to operate beyond the threshold time, it is necessary that:
- a) the airworthiness certification of the aeroplane type specifically permits operations beyond the threshold time, taking into account the aeroplane system design and reliability aspects;
- b) the reliability of the propulsion system is such that the risk of double power-unit failure from independent causes is extremely remote;
- c) any necessary special maintenance requirements are fulfilled;
- d) specific flight dispatch requirements are met;
- e) necessary in-flight operational procedures are established; and
- f) specific operational authorization is granted by the State of the Operator.
(ICAO Annex 6 Attachment E)
Attachment E goes on to discuss in some detail the correct interpretation of these requirements.
- ICAO Annex 6: Operation of Aircraft, Chapter 4, Section 4.7 and Attachment 'E';
- ICAO Doc 9760: Airworthiness Manual;
- JAR-OPS 1;
- UK CAA CAP513: Extended Range Twin Operations