ETOPS and Extended Diversion Time Operations

A twin-engined aeroplane that loses an engine must land at a suitable aerodrome within a reasonable time, because it now has no redundancy left in thrust and less in its systems. The rules therefore keep twins within a set flying time of an adequate aerodrome, and allow them further only under a specific approval. That approval, known as ETOPS, is what lets twins fly the oceans, the polar regions and remote continents.

The concept has grown beyond twins. ICAO calls it extended diversion time operations (EDTO), the FAA uses ETOPS for extended operations by twins and by passenger aeroplanes with more than two engines, and EASA keeps the term ETOPS. The principle is the same: a route may take the aircraft far from an aerodrome only if the aircraft, its maintenance, the planned alternates, the fuel and the crew can all support a long diversion.

What ETOPS means

ETOPS (extended-range twin-engine operations) began as a rule for twins. Today the FAA's Part 121 requires ETOPS approval, in operations specification B342, for a two-engined aeroplane on a route with any point more than 60 minutes from an adequate airport at the approved one-engine-inoperative cruise speed in still air and standard conditions. For passenger aeroplanes with more than two engines, ETOPS starts beyond 180 minutes. ICAO's extended diversion time operations (EDTO) apply the same logic to aeroplanes with two or more turbine engines, with the threshold time set by the State of the Operator.

EASA's limits without approval depend on the aeroplane (CAT.OP.MPA.140):

Beyond these, the operator needs a specific approval under Part-SPA. Approval levels are granted as a maximum diversion time for a particular aeroplane and engine combination: exam material quotes 90, 120, 138 and 180 minutes, and FAA approval levels are 75, 90, 120, 138, 180, 207 and 240 minutes and beyond. The aircraft type must first be found ETOPS-capable. The A320neo models, for example, are listed in the type certificate data sheet as capable when configured, maintained and operated to the ETOPS standard, but each operator still needs its own approval.

Threshold distance and rule time

The ETOPS threshold time is the flying time beyond which approval is needed, 60 minutes for the larger twins. The ETOPS threshold distance is the distance flown in that time in still air, in standard conditions, at the approved one-engine-inoperative cruise speed. At 400 kt it is 400 NM: if any point on the route is more than 400 NM from an adequate aerodrome, the flight is an ETOPS flight.

The ETOPS rule time is the maximum diversion time the authority has approved for the operator, written into its operations manual, and the rule distance is the corresponding distance at the same speed. With a 120-minute approval at 400 kt, every point on the route must lie within 800 NM of a suitable ETOPS alternate. On a map, circles of the rule distance are drawn around the alternates, and the route must stay inside them.

An adequate aerodrome for ETOPS is one expected to be available at the time of use, with a runway long enough, the necessary services (air traffic services, lighting, communications, weather reporting, navigation aids and rescue and fire-fighting cover) and at least one instrument approach aid. A suitable aerodrome is an adequate one whose weather and field conditions meet the planning minima on the day (see alternate aerodromes).

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ETOPS entry point and segments

Under 14 CFR 121.7 the ETOPS entry point (EEP) is the first point on the route more than 60 minutes' flying time, at one-engine-inoperative cruise speed in still air, from an adequate airport for a twin, or 180 minutes for a passenger aeroplane with more than two engines. The ETOPS segment runs from the entry point to the exit point, where the route comes back within the threshold distance; the diversion time limits apply within it.

Before the entry point the crew confirm that the ETOPS-significant systems are still serviceable, that the fuel on board still covers the critical fuel scenario and that the weather at the ETOPS alternates is still suitable, updating the plan with the dispatcher or operations centre if needed. If any of these fails, the flight re-routes or diverts before committing to the segment. In flight, equal time points between pairs of alternates tell the crew which way to turn after a failure; they depend on groundspeed, and a separate one is computed for an engine failure and for a depressurisation (see point of equal time and point of no return).

ETOPS alternates

An ETOPS alternate is an adequate aerodrome named in the flight plan for the ETOPS segment. It must lie within the approved diversion time, or within the shorter time imposed by the aircraft's MEL status on the day, and it must be suitable, its forecast at or above the ETOPS planning minima for the period in which the aeroplane might need it. The window and the minima depend on the rule set, and operators publish them in their operations manuals. In the European rule, SPA.ETOPS.115, the window runs from the anticipated time of landing until one hour after the latest possible time of landing, and the planning minima are the published minima plus these increments:

Under FAA rules (14 CFR 121.624) the ETOPS alternates are listed in the dispatch or flight release, must meet the ETOPS alternate minimums in the operator's specifications for the period from the earliest to the latest possible landing time, and must have adequate rescue and fire-fighting cover. If an alternate falls below minima after departure, the crew and dispatcher re-plan.

Primary airframe systems

ETOPS primary airframe systems are the systems with a fundamental influence on safety that could be affected by the shutdown of an engine: electrical power including the battery, hydraulics, pneumatics, flight instruments, fuel, flight controls, ice protection, engine start and ignition, propulsion instruments, navigation and communications, the APU, air conditioning and pressurisation, cargo fire suppression, emergency equipment and engine fire detection and extinguishing. They need redundancy, and the ETOPS MEL is more restrictive than the ordinary one: an item that can be deferred on a short sector may ground an ETOPS flight or shorten its diversion time.

Cargo fire protection shows how a system can set the diversion time. Under 14 CFR 121.633, the time needed to reach an ETOPS alternate may not exceed the most limiting cargo fire suppression time minus 15 minutes, left for the approach and landing. The maintenance programme supports the approval too: engine reliability, including in-flight shutdowns, is monitored continuously, and ETOPS-significant systems such as cargo smoke detection are tested regularly.

ETOPS critical fuel

The critical fuel scenario ensures that a failure at the worst place still leaves enough fuel to reach an alternate. Under 14 CFR 121.646, ETOPS critical fuel is the greatest of the fuel needed to fly from the most critical point to an ETOPS alternate after:

1. a rapid decompression, with a descent to a safe altitude;
2. a rapid decompression combined with an engine failure;
3. an engine failure alone, with drift-down to the one-engine-inoperative altitude.

To that are added a 5% allowance for errors in the forecast wind, fuel for icing or anti-ice, APU fuel where the APU must run, 15 minutes of holding at 1,500 ft, and an approach and landing. The aircraft departs with the greater of the critical fuel and the normal flight plan fuel, so on many sectors it adds nothing. A depressurised aeroplane cruising at low level burns fuel fast, which is why the decompression cases often set the figure. EASA meets the same need through additional fuel (see fuel planning and fuel reserves).

Redispatch and decision point

Long flights carry a large contingency allowance that is rarely used. Two procedures recover it. The FAA's redispatch releases a flag flight to an intermediate destination with full reserves; at the redispatch point, if the fuel remaining covers the rest of the route with reserves calculated from there, the dispatcher releases it onward to the final destination. This reduces the 10% en-route reserve of 121.645.

The European decision point procedure works the same way. Contingency fuel is carried only for the part of the route beyond a decision point, where an en-route alternate is available. At the decision point the crew check the fuel: if it covers the remaining trip plus contingency, the flight continues; otherwise it diverts. The largest saving is the contingency fuel between departure and the decision point, and the procedure is used only when the departure fuel gives a reasonable expectation of continuing. Either procedure lets an aircraft carry more payload, or fly a sector that full contingency would place beyond tank capacity.

Ultra long range operations

Ultra long range (ULR) operations are the longest non-stop sectors, many flown by twins under ETOPS. Their limits are human as much as technical. The duties exceed ordinary flight time limitation tables, so they are flown with augmented crews, in-flight rest in dedicated crew rest facilities, and fatigue risk management: under a fatigue risk management system approved under 14 CFR 117.7 in the United States, and within the operator's fatigue risk management under EASA's ORO.FTL.120. Fuel temperature is watched on long cold-soaked cruises, since Jet A-1 has a freezing point of −47 °C, and polar routes add communications largely limited to HF and few en-route alternates.

North Atlantic operations

Much ETOPS flying crosses the North Atlantic (NAT), and exam questions use it as the model. Transatlantic jets normally cross in the NAT High Level Airspace between FL285 and FL420, which requires State approval, two independent long-range navigation systems, RVSM approval and, between FL290 and FL410, data link; the daily organised track system, oceanic clearances and the strategic lateral offset procedure are described in oceanic and North Atlantic operations. All NAT aircraft monitor 121.5 MHz and the air-to-air frequency 123.45 MHz, the channels used when something goes wrong.

Oceanic contingency and weather deviation

An aircraft that cannot continue in accordance with its clearance first tries to obtain a revised one. If it cannot, the current ICAO contingency procedure in PANS-ATM and NAT Doc 007 applies:

• turn at least 30° left or right to establish a parallel, same-direction track offset by 5 NM from the cleared route;
• once established, either descend below FL290 and fly 500 ft offset from the normally used levels, or establish a vertical offset of 500 ft from those levels (1,000 ft if above FL410);
• broadcast the aircraft's identification, level, position and intentions at suitable intervals on the frequency in use and on 121.5 MHz (or, as a backup, 123.45 MHz), and watch for conflicting traffic.

The 45° turn and 15 NM offset of older texts no longer apply. An oceanic weather deviation is a separate procedure: the crew ask ATC first, by voice or CPDLC, and if no clearance can be obtained in time they deviate while broadcasting on 121.5 MHz and apply the level offsets NAT Doc 007 prescribes for weather deviations. A pressurisation failure calls for a rapid descent, with the level broadcast on 121.5 MHz.

RVSM contingency procedures

Between FL290 and FL410, RVSM separates aircraft by 1,000 ft. An RVSM aircraft needs two independent altimeters agreeing within 200 ft, an altitude alert with a threshold of no more than 300 ft, an autopilot with height hold and an altitude-reporting transponder, and ACAS is mandatory. The crew cross-check the altimeters before entering the oceanic area and report a difference of more than 200 ft. RVSM contingency procedures apply when that capability is lost: after a failure of required equipment, or in turbulence that prevents the aircraft from holding its level, the crew tell ATC they are unable RVSM and can expect a clearance out of the RVSM band or 2,000 ft of separation from other traffic.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.