While it may seem like an aircraft can simply fly “as the crow flies” – i.e. take the shortest path between its origin and destination – that’s not always the case. That’s because at any given point in flight, an aircraft is required to fly within a certain distance from an airport where it could land in a case of emergency.
For decades, the Federal Aviation Administration (FAA) in the United States required twin-engined aircraft to fly within 60 minutes of such airports. On some flights – especially overland ones – that wasn’t such an issue. On others – especially transoceanic ones – it could require a significant deviation from the shortest path, though.
That’s why ETOPS (Extended Twin Operations) regulations, which were crucial in the growth of transatlantic travel, were developed.
The Pre-ETOPS Times: The More Engines the Better
The first time that the FAA set rules about how far away from a diversion airport an airliner could fly was in the 1930s. Back then, aircraft were not as reliable as they are today.
As such, taking into account things like engine failure rate and single-engine cruise speed, it was decided that an aircraft could not fly further than 100 miles away from an airport where it could land in case of an emergency.
With improving technology and four-engined aircraft like the Lockheed Constellation being developed, the rule was relaxed a bit. Starting in 1953, the rule was only applicable to twin-engined aircraft. Also, the distance was not determined in miles anymore, but rather in the flight time required to reach the nearest alternate airport with one engine out.
Although individual exceptions could be granted, by default, that time was set at 60 minutes.
Around the same time, the International Civil Aviation Organization (ICAO) did its own research, and released a more relaxed set of guidelines. Based on these guidelines, an aircraft could be up to 90 minutes of flying at normal cruise speed (i.e. not at the slower single-engine cruise speed) away from a diversion airport.
These guidelines were adopted by many countries outside of the United States.
Still, the technology available at the time meant that even as the jet age came around, transatlantic travel was out of reach for twin-engine aircraft for years.
Instead, airlines used quadjets like the Boeing 707, Douglas DC-8, and the Boeing 747 for such flights. Those were later also joined by trijets like the Douglas DC-10 and the Lockheed L-1011.
The Beginnings of ETOPS: The 767 Goes Transatlantic
As reliable twinjets theoretically capable of crossing the Atlantic – like the A300, the 767, and the A310 – were developed in the 1970s and 1980s, airlines’ interest in using them for that purpose grew.
Doing so would allow them to save money on fuel compared to the three- and four-engined aircraft. Not only that, but their smaller size would also allow them to open routes with not enough demand to fill a larger aircraft like the 747.
In fact, some airlines started using the A300 on transatlantic flights – as well as others that involved significant overwater distances – in the mid-1970s.
Those flights were based on the 90-minute ICAO guidelines off-limits for U.S. airlines, though.
Instead, U.S. airlines wanting to fly their twins across the Atlantic, still bound by the “60-minute rule,” had to use considerably longer flight paths to stay close to airports like Kangerlussuaq in Greenland and Reykjavik in Iceland. That’s in spite of the fact that some of these airports were often unusable because of adverse weather conditions or the unavailability of ground services.
These developments caused the FAA to reconsider what was by that point a fairly archaic rule. The process was slightly slowed down by two twinjet incidents that occurred back-to-back in 1983.
The first of those was the infamous Air Canada “Gimli Glider” incident in which a 767 run out of fuel and lost power in both of its engines. The other one was United Airlines flight 310 operated by another 767 which had both of its engines overheat after flying through a thunderstorm. To solve that issue, the crew had to shut both of them down briefly.
In the end, however, it was argued that in the first case, the aircraft would have lost all of its power regardless of whether it had two, three, or four engines. In the latter case, it was argued that in spite of that incident, the probability of a double engine failure was negligibly low.
With that, the FAA introduced criteria for ETOPS-120 certification – i.e. for aircraft to be able to fly up to 120 minutes of single-engine cruise under standard conditions away from an alternate airport – in 1985. In February 1985, Trans World Airlines used one of its Boeing 767s to operatee the first ETOPS flight ever.
With the new regulation proving successful, at the end of 1988, the FAA expanded it and allowed aircraft manufacturers and airlines to apply for a certification of up to ETOPS-180.
Today’s ETOPS: Where There’s a Will There’s a Way
There are two levels at which ETOPS certification is provided. The first is the aircraft type-level (ETOPS type approval) and the second is the airline-level (ETOPS operational certification).
ETOPS type approval is granted to a certain aircraft type-engine combination once it is demonstrated that it is technically capable of flying with only single engine operational for extended periods of time. Of course, demonstrating that the probability of a failure of the second engine is extremely low is necessary as well.
There are four levels of type approvals: ETOPS-90, ETOPS-120 (can be extended 15% to ETOPS-138), ETOPS-180 (can be extended 15% to ETOPS-207), and ETOPS-180 to Design Limit. The last was introduced by the FAA in 2007 and allows U.S. registered aircraft to fly as far from diversion airports as they are technically capable of.
ETOPS operational certification is granted to a certain airline once it demonstrates that it has the necessary capabilities (engineering, procedures, etc.) to conduct ETOPS flights safely.
Since the certification process is lengthy and costly, only airlines that actually need it go through it. For example, Southwest Airlines only decided to do so recently in preparation for launching flights between the U.S. mainland and Hawaii which require ETOPS-180.
On the airline level, the ratings are more granular than on the type level. Airlines can apply for ETOPS-75, ETOPS-90, ETOPS-120/138, and ETOPS-180/207. In some cases, ETOPS-240, ETOPS-270, ETOPS-330, and ETOPS-370 are available on a case-by-case, route-specific basis as well.
If you love trijets and quadjets, you might despise ETOPS. After all, it’s easy to argue that it’s a regulation that is responsible for aircraft like the 747 and MD-11 losing their popularity among airlines. In reality, however, technological progress is the reason behind that.
ETOPS is just a regulation that allowed airlines to use that progress to operate smaller and less fuel-hungry twinjets even on long-haul routes. Thus, allowing for lower ticket prices as well as for non-stop flights between city pairs that could not generate enough demand for larger aircraft.
With ETOPS-120/138, two-engined aircraft can fly between any city pair that requires crossing of the North Atlantic. With ETOPS-180/207, they can fly above more than 90% of the Earth’s surface. And, with ETOPS-370 they can fly anywhere other than the remotest parts of Antarctica.
In other words, it’s because of ETOPS that airlines can offer safe, non-stop, and affordable flights on even the longest transoceanic routes flying over some of the most remote regions of the planet.