In the 1970s, 80s, and 90s tri-jet passenger planes were a core part of many commercial airline fleets. Aircraft like the McDonnell Douglas DC-10 and MD-11 had their role as high-capacity, long-haul jets for airlines like American Airlines, Swissair, Garuda Indonesia, and more. But while twin-jets, and to a lesser extent quad-jets, have been updated and re-released as newer versions over the last few decades, why are tri-jets no longer in-production? Let’s find out.
The first commercial tri-jets came in the 1960s from Hawker Siddeley and Boeing in the form of the HS-121 Trident and the 727, respectively. These aircraft were designed to offer long-range capabilities at a lower-capacity. One huge selling point for the 727 was its ability to take-off from shorter runways and therefore smaller airports. However, for the development and rise of larger tri-jets, ETOPS and civil aviation regulations were a driving force.
ETOPS regulations and the rise of tri-jets
One big driver for large tri-jet demand was what we now know as ETOPS regulations – or Extended-range Twin-engine Operational Performance Standards. The earliest variation was called the “60-minute rule” by the FAA.
These rules, adopted by civil aviation regulators, mandated that twin-jet aircraft were only permitted to fly on routes that are a set amount of single-engine flying time away from the nearest suitable airport. The rationale for this was that if one engine failed, there would be enough time to make an emergency landing at the nearest airport using the other remaining engine. As is obvious by the name of the first such rule, the initial time was set at 60 minutes.
In the 1950s, the ICAO (The International Civil Aviation Organization) recommended a 90-minute diversion time for all aircraft. This was adopted by many regulatory authorities and airlines outside the US (and FAA authority).
Of course, long-distance routes over oceans were impossible for twin-jets under these rules – thus requiring aircraft with more than two engines.
In 1964, however, the 60-minute rule was waived for three-engined aircraft. This opened the door for manufacturers to develop widebody, intercontinental tri-jets, including aircraft such as the McDonnell Douglas DC-10 and the Lockheed L-1011 Tristar.
With ETOPS allowing for tri-jets, aircraft with only three engines grew in popularity for intercontinental operations, often being chosen over four-engined aircraft. This was because three-engined aircraft were more fuel-efficient.
Indeed, three-engined widebodies were seen as the ‘sweet-spot’ between twin and quad-jet aircraft, having better range, payload capabilities, and capacity than twin-jets, without the excessive fuel consumption of quad-jets.
ETOPS and the fall of tri-jets
While early ETOPS was partially responsible for the rise of large tri-jets, later updates to these rules would be part of their downfall.
From the 1980s and onwards, we would see ETOPS rules go from 60 minutes to 120 minutes, and up to 180 minutes at the end of the decade. While ratings would only continue to go up in subsequent decades, ETOPS-180 was enough for manufacturers to shift their development towards long-range twin-jets.
It was during this period that we would see the rise of the Airbus A310 and the Boeing 767 – both of which were long-range twin-jets capable of transatlantic operations.
Four, three, two
For the same reason carriers made shifts from four-engined aircraft towards three-engined aircraft, airlines also shifted from three-engines to two: lower-costs and greater efficiency.
For tri-jets, it wasn’t just in terms of operation and maintenance – it also extended to the cost of manufacturing. Tri-jets came with a higher purchase price due to the additional engine and the complexity of mounting it through the tail.
Thus, as competitors like Boeing and Airbus were offering more efficient twin-jets with a range comparable to the DC-10 (and later the MD-11), airlines were drawn to these newer jets that offered cost-savings. This is why the Boeing 777 has become one of the most popular widebodies ever with over 2000 orders to date.
This is the same reason we are now seeing the decline of quad-jets. Airbus recently ended production of their superjumbo A380 while Boeing is at a crossroads, needing to decide soon if it will continue its 747 production line. While the downfall of four-engined aircraft has been much, much slower, the arguments have been similar to those against tri-jets: Twin-jets offer better fuel economy and lower maintenance costs.
Are we missing anything with tri-jets?
So now that tri-jets are gone from the commercial passenger sector of aviation, are we actually missing anything that twin-jets can’t offer?
For the most part, no – we aren’t missing much with the disappearance of the tri-jet. Twin-jets offer the same levels of comfort, performance and, with new technologies we are seeing even more efficiency.
However, the key value of tri-jets or quad-jets these days – at least for some travelers – is the peace of mind that comes with additional engines. Despite ETOPS regulations, specifications, and ratings, It might make nervous passengers feel better to have additional engines in case one… or two, experience a failure. Of course, statistically, it is extremely rare to have a catastrophic crash these days due to the failure of two engines.
So do you think tri-jets have a place in modern commercial aviation? Or are these types of aircraft strictly a thing of the past now? Let us know your thoughts in the comments.