Definition

Extended Diversion Time Operations (EDTO) is defined as international flights by transport category airplanes with two or more turbine engines where the diversion time to an en route alternate airport is greater than 60 minutes, and/or the threshold time established by the State of the Operator.

EDTO offers a measure of efficiency. On a long flight, particularly over a vast ocean, an aircraft might need to fly a longer route than a straight course to the destination to remain within 60 minutes of a diversion airport. But if approved for EDTO, the aircraft can fly a shorter, straight-line route (or at least a more direct route), as depicted in the graphic below.

Flights of such distance can require as many as three different kinds of diversion, or alternate airports:

• Takeoff Alternate - an alternate airport where an aircraft can land in an emergency shortly after departure when it is not possible to return to the airport of departure.
• En Route Alternate - an alternate airport where an aircraft can land in an emergency while en route. A long flight can include multiple en route alternates.
• Destination Alternate - an alternate airport where an aircraft can land if it becomes impossible or inadvisable to land at the intended destination.

Depending on operational need and aircraft capability, flights beyond threshold time can be approved at different levels:

• Up to 90-minute authorization.
• Beyond 90 minutes and up to 180 minutes.
• Beyond 180 minutes.
• Fifteen percent diversion time increases for specific routes.

Background

Changes to International Civil Aviation Organisation (ICAO) Annex 6 Part 1 introduced EDTO as a replacement for what was previously known as Extended Range Operations (ETOPS), which applied to twin-engine aircraft. The new program expands the concept to include aircraft with more than two engines. However, the two phrases have been used somewhat interchangeably.

According to ICAO Doc 10085, "Extended Diversion Time Operations Manual," there are no additional maintenance or certification requirements for airplanes with more than two engines. "This means that for EDTO with more than two engines, neither the basic type certification nor the maintenance programme needs to be reviewed, as both remain valid for EDTO operations," the EDTO manual says.

The manual lists detailed requirements for EDTO flights. They include:

• Aircraft airworthiness considerations
• EDTO flight operations requirements
• EDTO maintenance and reliability requirements

These considerations include potentially time-limiting items such as cargo fire suppression systems, engine fire suppression systems, and electrical systems including battery capability. Other issues include aircraft performance such as drift-down distances, engine-out speed schedules, and fuel consumption.

The EDTO Operational Approval Process

An applicant for EDTO Operational Approval must apply in the manner specified by the State of the Operator. The type of approval process which is then followed will depend on whether the applicant has direct in-service experience with the candidate aircraft, for example one year of non-EDTO operations for a 120 minute twin engine approval or one year of 120 minutes EDTO operations for a 180 minute twin engine approval, or not. With such experience, the 'In-service' (formerly called 'Conventional)' track is followed to develop a simplified Approval Plan but if an applicant is unable to demonstrate such prior experience then the longer 'Accelerated EDTO' approval track will apply.

Any applicant will be expected to:

• Define the EDTO routes that will be covered by application.
• For the aeroplane type to be used, establish EDTO maintenance procedures (including but not limited to appropriate engine condition, IFSD and oil consumption monitoring and validation of APU start reliability).
• For each proposed route, establish a list of adequate en-route alternate airports (requirements include but are not limited to the availability of at least one approach aid and a minimum [Rescue and Fire Fighting Category] of 4.
• Determine the EDTO diversion time required and the EDTO engine inoperative planning speed.
• Establish the required EDTO Area of Operations.
• Establish a system for obtaining EDTO flight plan data i.e. EDTO en-route alternates, equal time points, the critical fuel scenario and time limited systems.
• Make arrangements to obtain weather data for EDTO en-route alternates.
• Ensure there is a reliable method of communication between the aeroplane and the airline during the flight.
• Review the EDTO provisions in the approved MMEL in order to establish the airline MEL for EDTO.
• Establish a method of checking the in-flight start reliability of the APU.
• Designate an EDTO Check Pilot.
• Establish and fully document airline operating procedures for EDTO in EDTO Procedures Manuals for both Flight Operations and Maintenance processes.
• Expand normal flight crew and aeroplane maintenance guidance material to include EDTO practices and procedures.
• Establish appropriate EDTO training procedures for line maintenance and flight operations ground staff and for flight crew.

Before issuing an EDTO approval, a State must normally ensure that the maximum diversion time for the operator of a particular aeroplane type does not exceed the most limiting EDTO-significant-system time limitation which is relevant to that particular operation and identified in the AFM (directly or by reference) is not exceeded and, in the case of aeroplanes with two turbine engines only, that the aeroplane type involved is EDTO certified. However, if a specific safety risk assessment conducted by the aeroplane operator has demonstrated to the satisfaction of the State that an equivalent level of safety can be maintained during operations beyond the time limits of the most time-limited system, then there is discretion to approve such an operation. The specific safety risk assessment required to allow this exceptional EDTO approval to be granted must:

• describe the capabilities of the operator
• provide data which demonstrates the overall reliability of the aeroplane
• assess the reliability of each time-limited system
• provide relevant information from the aeroplane manufacturer
• detail any specific mitigation measures

A representation of the EDTO regulatory regime (Source ICAO)

Any EDTO approval issued by a State must also reference the need for compliance with the EDTO critical fuel scenario established by the State and any flight conducted under an EDTO approval must not continue beyond the specified Threshold Time until the identified alternates have been re-evaluated for their continued availability and current information indicates that, during the period of time when their use might be required, the prevailing conditions at those aerodromes will not be less than the applicable aerodrome operating minima. If this is not the case, then an alternative course of action, which does not involve exceeding the applicable Threshold Time must be determined.

Approvals for aeroplanes with two turbine engines are also required to take into account the following when determining if such an approval will provide the overall level of safety for any flight intended by the provisions of ICAO Annex 8 in respect of:

• the reliability of the propulsion system
• the airworthiness certification of the aeroplane type
• the EDTO-specific maintenance programme

U.S. Guidance

The U.S. Federal Aviation Administration's (FAA) Advisory Circular 120-42B covers extended-range airline operations by twin-engine aircraft and aircraft with more than two engines. The document says the FAA may authorize extended-range operations with two-engine airplanes over a route that contains a point farther than 60 minutes flying time from an adequate airport at an approved one-engine inoperative cruise speed under standard conditions in still air. The document further states that the FAA may authorize extended-range operations with passenger airplanes with more than two engines over a route that contains a point farther than 180 minutes flying time from an adequate airport.

For U.S. operators to fly extended-range routes, ETOPS must be authorized in the carrier's Operations Specifications and conducted in compliance with the OpsSpecs. ETOPS requirements must be specified in the company's maintenance and operations programs. The requirements include stipulations for a Continuous Airworthiness Maintenance Program (CAMP) and certain pre-departure service checks (PDSCs). AC 120-42B carries the following note:

Proper servicing of fluids, such as engine, APU, generator systems, and hydraulic systems is a vital ingredient to successful ETOPS operations. Some current ETOPS operators have had incidents resulting from improper fluid servicing, or not properly determining or addressing high consumption rates. This has resulted in [in-flight shutdowns] and diversions. Certificate holders should consider this area very seriously when developing their maintenance checks, including the [pre-departure service check]. 

For Part 135 operators, generally considered to be commuter and on-demand operations, the relevant ETOPS guidance comes under Advisory Circular 135-42, "Extended Operations (ETOPS) and Operations in the North Polar Area."

That document includes a number of requirements. A partial list:

• Airplanes manufactured after February 15, 2015 must be certified for ETOPS. Aircraft manufactured before that date do not need to be type designed, but should be "acceptable to the Administrator."
• Part 135 certificate holders must have at least 12 months experience operating a transport-category multi-engine airplane in international operations (excluding Canada and Mexico). Operations to or from Hawaii may be considered experience in international operations.
• Certificate holders should ensure ETOPS airplanes are maintained and equipped to recommended standards and practices.
• Certificate holders should ensure flight crew and maintenance personnel are properly trained and qualified in all aspects of ETOPS.
• Certificate holders should develop a minimum equipment list (MEL) that reflects the unique aspects of ETOPS for each type of airplane.

Flight crew training requirements include areas such as:

• Review of representative routes and airports within ETOPS area of operation.
• Procedures for determining, before entry into an ETOPS area of operation, that critical systems and components are operating within normal parameters.
• Flight preparation, such as alternate airports, in-flight weather updates, the uncertainty of long-term forecasts, fuel/oil requirements including calculations for reserves, flight progress monitoring, and timely diversion decisions.

Further Reading

• ICAO Doc 10085, "Extended Diversion Time Operations Manual," First Edition, 2017.
• FAA Advisory Circular 120-42B, "Extended Range Operations (ETOPS and Polar Operations)," 2008.
• FAA Advisory Circular 135-42, "Extended Operations (ETOPS) and Operations in the North Polar Area," 2008.