071 Operational Procedures topic guide
ETOPS Explained
A twin-engined aeroplane that loses an engine has one option a four-engined aeroplane rarely needs to think about as urgently: get to a runway. Extended-range operations with two-engined aeroplanes, universally shortened to ETOPS, exist because regulators drew a line under how far a twin may fly from a suitable diversion aerodrome unless the operator, crew, and aeroplane have been specifically approved to go further.
The classic reference point is a diversion time of 60 minutes, flown at the approved one-engine-inoperative cruise speed in still air. Beyond that, without ETOPS approval, the route simply is not available to a twin. With ETOPS approval, the same aeroplane can plan routes where the diversion time reaches values such as 120 minutes or 180 minutes and beyond, provided the extra reliability, procedures, and fuel planning that approval demands are all in place.
What the diversion time actually measures
The diversion time is not a straight-line distance on a chart. It is the time it would take the aeroplane to fly, in still air, from the point on the planned track that is furthest from a diversion aerodrome, to that aerodrome, using the speed approved for one-engine-inoperative cruise. Wind is deliberately excluded from the definition itself; the still-air assumption keeps the rule consistent regardless of what the wind happens to be doing on the day, while fuel planning for the actual flight still accounts for the forecast wind separately.
Because the speed used is the reduced, one-engine-inoperative speed rather than the normal all-engines cruise speed, the diversion time for a given distance is longer than a quick mental estimate at cruise speed would suggest. This is one of the more common traps: plugging in the normal cruise speed instead of the approved OEI speed understates the true diversion time and can make an ineligible route look eligible.
Adequate and suitable aerodromes
ETOPS planning distinguishes between an aerodrome that is merely adequate and one that is suitable for the specific flight. An adequate aerodrome is one that meets the aeroplane's performance requirements and is available and equipped to a standard that would support a landing, considered in general terms rather than for one particular day.
A suitable aerodrome takes that same adequate aerodrome and asks whether it will actually work at the expected time of use: is the weather forecast to be at or above the applicable minima, and are the runway and field conditions usable. An aerodrome can be adequate all year round and still fail to be suitable for a specific departure because of forecast fog, a closed runway, or contamination the crew cannot accept on the day.
- Entry point: where the route joins the ETOPS-critical segment beyond the standard, unrestricted diversion time
- ETOPS segment: the portion of the route flown beyond that threshold
- Exit point: where the route rejoins a segment within the standard diversion time
- Adequate aerodrome: meets performance and equipment standards in general
- Suitable aerodrome: adequate, and forecast to be usable at the expected time of use
Worked example
Worked example: recognising an ETOPS segment
Not quite. The correct answer is B.
Correct answer: B
- A. There is no allowance for rounding down to the threshold. Exceeding the 60-minute reference without approval is exactly the situation the rule exists to prevent.
- B. Correct: once the still-air, OEI-speed diversion time to the nearest adequate diversion aerodrome exceeds the standard threshold, the flight is outside unrestricted twin-engined operation and needs ETOPS approval covering that diversion time.
- C. The diversion time is defined in still air specifically so that a favourable forecast wind cannot be used to justify an otherwise non-compliant route.
- D. ETOPS approval is a planning requirement decided before dispatch, based on the route's worst-case diversion time, not a reactive requirement triggered only if a failure happens.
Step by step
- Compare the quoted diversion time, 70 minutes, against the classic 60-minute reference threshold for unrestricted twin-engined operation.
- Confirm the time was computed in still air at the approved OEI speed, which is the only basis the rule recognises.
- Since 70 minutes exceeds 60 minutes, the aeroplane needs ETOPS approval covering at least that diversion time before the route can be planned.
- Note that this decision is made at the planning stage, independent of whether an engine failure ever actually occurs on the day.
Common mistakes
Using normal cruise speed instead of the approved OEI speed for the diversion time
This understates the true diversion time and can make a route look compliant when it actually needs ETOPS approval, which is a dispatch-planning error, not a rounding error.
Treating an adequate aerodrome as automatically suitable
An aerodrome that meets the general performance and equipment standard can still be unusable on the day if the forecast weather or field condition fails the suitability test, and planning against it anyway removes a genuine diversion option.
Applying forecast wind to the diversion-time definition itself
The diversion time that decides whether ETOPS approval is needed is a still-air figure. Confusing it with the wind-corrected time used for actual fuel planning produces the wrong compliance answer even if the fuel figures are otherwise fine.
Related topic guides
Practise Operational Procedures the way the exam asks it.
SkyStudy turns ETOPS Explained and every other Operational Procedures topic into exam-style practice questions with explanations, spaced repetition, and timed mock exams. Free to start.
Important information
This page is general educational information for student pilots and may be out of date.
Aviation rules, training requirements, costs, medical standards, and exam details change over time and vary by country, authority, and training organisation, so details here may no longer be current or may differ in your case.
Always confirm the current details with your approved training organisation (ATO) and national aviation authority before relying on them.
SkyStudy is an independent study aid, is not affiliated with EASA or any aviation authority, and does not guarantee any exam or licence outcome.
Last reviewed July 2026