ETOPS explained: long-haul with two engines and diversion airports

An Airbus A350 on its way from Europe to the US West Coast, a Boeing 787 over the Pacific, an A330 over the Indian Ocean: that twin-engine jets today fly across oceans as a matter of course is thanks to a set of rules called ETOPS. It determines how far a twinjet may be from a suitable airport and what requirements the aircraft, airline and flight planning have to meet for that. This article explains the minute tiers, the history behind them, the fuel rules and why ETOPS is interesting for spotters at diversion airports.

ETOPS: the short answer

ETOPS stands for Extended-range Twin-engine Operations Performance Standards. It refers to special rules for twin-engine airliners that, on their route, are more than 60 minutes of single-engine flight from a suitable airport. The number after the acronym gives the maximum permitted diversion time: an aircraft with ETOPS-180 may not be more than 180 minutes from an approved diversion airport at any point on the route, calculated with only one engine running in still air.

Behind this simple formula lies an entire system: the aircraft type needs a matching type approval, the airline an operational approval from its authority, and every flight is prepared with specific diversion airports, weather checks and additional fuel. ICAO has meanwhile adopted the term EDTO (Extended Diversion Time Operations) for the concept, which includes aircraft with two or more turbine engines. In practice and among spotters, though, ETOPS is still the common word.

Why ETOPS exists at all

The idea behind it is simple: if an engine fails on a twin-engine aircraft, the rest of the flight depends on a single powerplant. A four-engine aircraft like the Boeing 747 or a three-engine aircraft like the DC-10 still has reserves in that case. That is why strict distance rules applied to twinjets for a long time.

In the US, the aviation authority introduced a 60-minute rule as early as 1953: twin-engine airliners were not allowed to be more than one hour of flight on one engine from a suitable airport. ICAO recommended 90 minutes at the time, which many other countries adopted. For Atlantic or Pacific flights, twins were thus practically ruled out. Anyone who wanted to cross the ocean needed three or four engines.

With modern turbofan engines, the situation changed. The powerplants became so reliable that a failure at cruise altitude became very rare. At the same time, types such as the Airbus A300-600 and the Boeing 767 brought ranges sufficient for transatlantic routes. The airlines only lacked permission. ETOPS was the answer: no longer a blanket ban but an approval under clearly defined conditions.

The history in stages

The diversion times were not released all at once but expanded step by step – each time after the previous tier had proven itself in service.

Year	Step	Meaning
1953	60-minute rule in the US	twins stay near the coast, ocean routes are reserved for multi-engine aircraft
1985	FAA allows 120 minutes	TWA starts ETOPS-120 flights on February 1, 1985, the North Atlantic opens up to twins
1988	FAA allows 180 minutes	large parts of the Atlantic and Pacific become reachable for twinjets
1995	Boeing 777 with “Early ETOPS”	a new type starts directly with a 180-minute approval instead of after years of proving itself
2007	FAA rules for more than 180 minutes	approvals up to the design limit of the type; three- and four-engine aircraft also fall under the rules beyond 180 minutes
2009	A330 with ETOPS-240	first type with a 240-minute approval
2011–2014	777 and 787 with 330 minutes	Boeing extends the type approvals of its long-haul twins
2014	A350 with up to 370 minutes	EASA grants the approval even before entry into service

At the historic TWA, regular Atlantic operations under ETOPS-120 began with a Boeing 767-200 between Boston and Paris. That was the starting signal for a development that fundamentally changed long-haul flying. You will find more about the manufacturers behind the types in the profiles of Airbus and Boeing.

The minute tiers at a glance

The number after ETOPS is not a guarantee for a particular route but an upper limit. How far an airline may actually go depends on the lowest of three approvals: type approval, operational approval and the system limits of the specific aircraft.

Tier	Typical use	Special feature
ETOPS-75 / 90	regional overwater routes, for example in the Caribbean or Micronesia	lowest requirements for type and operation
ETOPS-120	North Atlantic on more southerly routes, Mediterranean and coastal routes	classic entry tier of the 1980s
ETOPS-138	North Atlantic	120 minutes plus about 15 percent, when a diversion airport is temporarily unavailable
ETOPS-180	large parts of the Atlantic and Pacific	covers most of the world’s long-haul routes
ETOPS-207	North Pacific	in the US rules as a flight-by-flight exception when no diversion airport is available within 180 minutes
ETOPS-240 and more	South Pacific, South Atlantic, Indian Ocean, polar regions	only with experience at lower tiers and for defined areas or city pairs

The difference between minutes and kilometers is important. The diversion time is calculated at cruise speed with one engine out. An aircraft that flies faster on one engine covers a greater distance in 180 minutes than a slower one. On the map, this produces a circle around each diversion airport, and the route has to run through these circles without gaps.

Three levels: aircraft, airline, flight

ETOPS is not a label that an aircraft receives once and then keeps. The approval is made up of three building blocks that have to fit together.

How flight planning works in detail and what role the dispatcher plays is covered in the article on flight dispatchers.

Engine reliability in numbers

Target values apply to type approval for so-called in-flight shutdowns, meaning engine shutdowns in flight. The higher the ETOPS tier, the more rarely they may occur: for 120 minutes the bar is fewer than one shutdown per 20,000 engine hours, for 180 minutes fewer than one per 50,000 hours and beyond 180 minutes fewer than one per 100,000 hours. Airlines have to record their figures continuously. If the statistics deteriorate, the authority can downgrade or suspend the approval.

Fuel: the critical scenario

Every scheduled flight carries reserves. With ETOPS an additional calculation is added: the planning assumes that something goes wrong at the least favorable point of the route, and checks whether the fuel then lasts to the diversion airport. In the US rules, three cases are worked through for this, and the most demanding one determines the amount:

• Loss of cabin pressure: The aircraft has to descend to a low altitude at which passengers can manage without oxygen masks. In dense air, engines burn significantly more fuel – this case is often the most expensive.
• Pressure loss and engine failure at the same time: The combination of low altitude and only one engine.
• Engine failure alone: The aircraft descends to single-engine cruise altitude and continues at reduced speed.

On top of the result come allowances: five percent more headwind than forecast, fuel for ice protection, a buffer for aged engines and, at the diversion airport, 15 minutes of holding at 1,500 ft above field elevation plus approach and landing. If the auxiliary power unit (APU) is required as a power source, its consumption is also included.

Diversion airports: what they have to offer

An ETOPS diversion airport is not just any runway nearby. It has to be suitable for the type, be listed as a diversion destination in the airline’s documents and be open at the possible arrival time. According to ICAO requirements, it needs at least one approach aid and an airport fire service of at least category 4. Before the flight and once more before entering the ETOPS area, the crew checks whether the forecast weather there meets the minimum conditions.

The moment from which a flight is more than 60 minutes from a suitable airport is called the ETOPS entry point. From here the special rules apply. On the North Atlantic, the typical diversion destinations lie at the edges of the ocean and on the islands in between: in Canada, on Greenland, on the Azores, in Ireland and in Iceland. Keflavik Airport and Shannon Airport are examples of airports that qualify for such diversions thanks to long runways and their location on the Atlantic.

Polar routes bring additional requirements. The US rules require, among other things, a plan for how stranded passengers are looked after at remote diversion airports, a strategy against fuel freezing and cold-weather protective suits on board.

How ETOPS changed long-haul flying

Before twins were allowed over oceans, three- and four-engine aircraft shaped long-haul flying. With every ETOPS extension the balance shifted. Two engines mean lower fuel consumption and less maintenance than four. That made twinjets more economical on many routes – first on the North Atlantic, later over the Pacific and the Southern Hemisphere too.

Today a large share of long-haul flights is flown with types such as the Airbus A350-900, the Boeing 787-9, the Boeing 777-300ER or the Airbus A330-300. The four-engine Airbus A340-300 was attractive for a long time precisely because it did not fall under the twin rules. How to tell it apart from the outwardly similar A330 is shown in the guide A330 or A340?, and for the two modern long-haul twins the comparison A350 or Boeing 787? helps.

Narrowbody jets use ETOPS too. The historic Aloha Airlines deployed Boeing 737-700s with a 180-minute approval between Hawaii and the North American mainland. Today long-range narrowbodies such as the Airbus A321XLR bring twin overwater flights even to routes for which a widebody was once necessary. How far modern aircraft get nonstop is shown in the article on ultra-long-haul flights.

ETOPS and the route on the map

If you follow an Atlantic flight on a live map, you often see an arc to the north. The main reason is geometry: the shortest connection on a sphere is the great circle, which looks curved on flat maps. The article Why aircraft fly in arcs explains that. For twinjets a second condition is added: the route has to lie within the ETOPS circles around the diversion airports. With 180 minutes and more, that is no obstacle on most routes. At lower tiers or in remote regions, however, the permitted route can deviate noticeably from the shortest one.

What this means for spotters

For spotters, ETOPS is visible mainly in one place: diversions. If a long-haul flight over the ocean has to divert, it lands at one of the diversion airports designated in advance. There, types and airlines show up that do not appear in the regular schedule. How such diversions come about is described in the article Diversion to an alternate airport, and how to spot them live is in the guide Spotting diversions and alternate landings.

Not every diversion has to do with an engine. Common reasons are medical emergencies on board, technical messages from other systems or the weather at the destination. An emergency squawk such as 7700 on flight tracking is a clue but not a diagnosis – what the codes mean is explained in the article Squawk codes 7500, 7600 and 7700.

What to keep in mind

• The number is an upper limit. ETOPS-370 does not mean an A350 regularly flies six hours from any airport. Most routes get by with considerably smaller values.
• Type approval is not operational approval. An aircraft type can be approved for high values while a particular airline may only use lower tiers.
• ETOPS and EDTO mean the same principle. If you read EDTO in technical texts, it is the same concept under the newer ICAO name.
• Don’t interpret diversions too quickly. Whether an engine was the reason is only shown by an official statement or an investigation report – not the kink in the course on the map.
• The joke about the acronym. Among pilots the expansion “Engines Turn Or Passengers Swim” goes around. Funny, but the statistics of twinjets have told a different story for decades.

Conclusion

ETOPS turned a blanket ban into a controlled approval. Twin-engine airliners may stray far from airports if type, airline and flight planning jointly demonstrate that the failure of an engine remains manageable at every point on the route. Since the first 120-minute flights in 1985, the limits have grown step by step – up to the A350’s 370 minutes. For you as a spotter, the system becomes visible mainly when a long-haul jet lands at a diversion airport where it otherwise never shows up.