Extended Diversion Time Operations (EDTO)


Before we discuss what is EDTO (ETOPS), one statement should be understood at the beginning:

Aeroplanes with turbine engines operating beyond 60 minutes to an en-route alternate aerodrome are not required to have specific additional approval by CAD except if they engage in EDTO.

So, what is EDTO?

Extended Diversion Time Operations (EDTO) refers to any operation by appropriately qualified flight crew on an aeroplane with two or more turbine engines and at the approved airspeed (OEI/AEO) of which the diversion time to an en-route alternate aerodrome is greater than the threshold time established by CAD.


For all twin-turbine engined aeroplanes which are flying for the purpose of public transport, with maximum authorized take-off weight exceeds 5,700 kg and certificated to carry more than 19 passengers, and requires to fly more than a threshold time of 60 minutes (calculated at One Engine Inoperative (OEI) cruise speed in still air and International Standard Atmosphere (ISA) conditions) from an en-route alternate aerodrome; or
all aeroplanes with three or more turbine engines which are flying for the purpose of public transport and require to fly more than a threshold time of 180 minutes flight time (calculated at an All Engines Operative (AEO) cruise speed in still air and ISA conditions) from an en-route alternate aerodrome;

Okay, at the moment we should understand that if it is no need to fly beyond aircraft type specific diversion time – literally the range, expressed in time – then no need special (EDTO) approval!

However, considering various factors in relation to the aircraft currently registered in Hong Kong, the threshold time set for twin turbine-engined aeroplanes is 60 minutes unless otherwise stated.


EDTO is a terminology, which is defined according to ICAO Annex 6 Part I, found later than ETOPS. For more details, read trailing content in this article.

Next, what is the difference between EDTO and ETOPS?

EDTO vis-a-vis ETOPS

Extended Range Twin Operations (ETOPS) enable properly certificated twin-engined aeroplanes operated by appropriately qualified flight crew to fly further than a threshold time of 60 minutes at One Engine Inoperative (OEI) cruise speed. In accordance with International Civil Aviation Organization (ICAO) Annex 6 Part I, such requirement is renamed as Extended Diversion Time Operations (EDTO) and is expanded to include the operation of aeroplanes with three and four engines.


Elements of an EDTO OPS assessment

  1. Operations         (Operational approval)
  2. Maintenance     (Operational approval)
  3. Design                (Type design & reliability approval)
  4. Reliability          (Type design & reliability approval)

In general, ETOPS operational approval is the responsibility of AOC holder (carrier/airline); and ETOPS Type design and reliability approval is the responsibility of aircraft manufacture. Both AOC holder and aircraft manufacture should demonstrate their compliance to the standards listed on ICAO Annex and different manuals as well as documents of local civil aviation authority.



In Hong Kong, the corresponding EDTO operations must be so approved in accordance with the requirements stipulated in CAD513

ETOPS is considered as equivalent to EDTO for twin-turbine engined aeroplanes. Operators with ETOPS Approval DO NOT require to apply for EDTO Approval for the same aeroplane airframe/engine combinations and on the same routes and to the same maximum diversion time as was authorised for ETOPS. The previous edition of CAD 513, which details the corresponding provisions for ETOPS, is considered as an acceptable mean of compliance to the requirements for EDTO for twin-engined aeroplanes. Therefore they are maintained and adopted in this document as Section II Sub-Section B.

Section I 4.2: The maximum diversion time is the range (expressed in time) from a point on a route to an en-route alternate aerodrome up to which CAD will grant approval. The following factors will also be considered in conjunction with other requirements stipulated in this document:
(a) for all aeroplanes: the most limiting EDTO significant system time limitation, if any, indicated in the aeroplane flight manual (directly or by reference) and relevant to that particular operation is not exceeded; and

Notwithstanding the provisions in paragraph 4.2(a) of Section I, the CAD may, based on the results of a specific safety risk assessment conducted by the operator which demonstrates how an equivalent level of safety will be maintained, approve operations beyond the time limits of the most time-limited system. The specific safety risk assessment shall include at least the:
(a) capabilities of the operator;
(b) overall reliability of the aeroplane;
(c) reliability of each time-limited system;
(d) relevant information from the aeroplane manufacturer; and
(e) specific mitigation measures.


EDTO significant system (time-limiting)

The capability of Time Limited System must be considered at dispatch for the purpose of identification and selection of en- route alternates (verification of weather). The maximum diversion time should not exceed the value of the EDTO significant system limitation(s), if any, for EDTO identified in the Aeroplane’s Flight Manual directly or by reference, reduced with an operational safety margin, commonly 15 minutes, specified by the CAD.

Most Time Limited System ≥ EDTO maximum diversion time + 15 min

Notes: EDTO  significant system is divided into: 1) time-limiting system and 2) non-time limiting system. For example, there is requirement that a sufficient number of reliable – three independent electrical power sources should be available to meet the requirements of JAR 25.1309.


For aeroplanes engaged in EDTO, the additional fuel required by CAD360 Part I Chapter 4 shall include the fuel necessary to comply with the EDTO critical fuel scenario.

The following should be considered, using the anticipated mass of the aeroplane, in determining the corresponding EDTO critical fuel:

(a) fuel sufficient to fly to an en-route alternate aerodrome, considering at the most critical point of the route, failure of one engine or simultaneous engine failure and depressurization or depressurization alone, whichever is more limiting (see paragraph 9 of this Sub-Section)

(b) fuel to account for icing;

(c) fuel to account for errors in wind forecasting;
(d) fuel to account for holding, an instrument approach and landing at the en-route alternate aerodrome;
(e) fuel to account for deterioration in cruise fuel burn performance; and
(f) fuel to account for APU use (if required)

The following factors may be considered in determining if a landing at a given aerodrome is the more appropriate course of action:

(a) aeroplane configuration, weight, systems status, and fuel remaining;
(b) wind and weather conditions en-route at the diversion altitude, minimum altitudes en- route and fuel consumption to the en-route alternate aerodrome;
(c) runways available, runway surface condition, weather, wind, and terrain, in proximity of the en-route alternate aerodrome; and
(d) instrument approaches and approach/runway lighting available, rescue and fire fighting services (RFFS) at the en-route alternate aerodrome;
(e) pilot’s familiarity with that aerodrome and information about that aerodrome provided to the pilot by the operator; and
(f) facilities for passenger and crew disembarkation and accommodation.


EDTO Approval Route Planning – 4 basic steps

  1. Selection of Desired Routes
  2. Selection of adequate En-route alternate airports
  3. Diversion Distance Determination
    – Diversion Time Required
    – Engine Inoperative Speed Selection
    – Reference Weight
  4. Critical Fuel Estimates



Adequate Airport

  • available (serviceable)
  • performance requirements for the expected landing weight
  • Weather
  • navigation aid
  • ground operational services
  • emergency services (RFF)


About is a list showing part of the requirements. In short, in EDTO operations, there are three basic elements as the engine inoperative diversion strategies.

Engine Inoperative Diversion Strategies

  1. Obstacle Clearance
  2. Fuel
  3. Speed (Distance cover and Flight Time)

Please be reminded that “Strategy” is defined in terms of a diversion speed. The chosen speed (which will be approved) will have an impact on the diversion distance and the fuel consumption. So, to be more easy to understand, we could comprehend: the crews should choose a “best” diversion speed to make a safe landing at suitable alternate aerodrome. The  “best” diversion speed should take the three elements into consideration (obstacle clearance, fuel remain and distance cover (that related to flight time as well as speed).


Last but not least, training is important in EDTO operations.

Generally speaking, the training is covering various areas:

  • EDTO rules
  • Flight Planning (route selection, alternate airport requirements, fuel requirement)
  • Dispatch release (MEL)
  • En-route procedure
  • Diversion decision (Engine INOP Diversion Strategy)



What’s Alternate aerodrome

Alternate aerodrome is an aerodrome that an aircraft may proceed where aircraft performance requirements can be met and which is expected to be operational if required.

(3) Three types of Alternate aerodrome

  1. Take-off alternate
  2. En-route alternate
  3. Destination alternate

Take-off alternate refers to an alternate aerodrome at which an aircraft would be able to land should this become necessary shortly after take-off and it is not possible to use the aerodrome of departure.


What’s Threshold time
The range, expressed in time, established by CAD to an en-route alternate aerodrome, whereby any time beyond requires an EDTO Approval from CAD.

What’s Maximum diversion time
Maximum allowable range, expressed in time, from a point on a route to an en-route alternate aerodrome.

What’s Point of no return
The last possible geographic point at which an aeroplane can proceed to the destination aerodrome as well as to an available en-route alternate aerodrome for a given flight.



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