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 why are tri-jets no longer in-production today? 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. However, for the development and rise of larger tri-jets,
ETOPS and civil aviation regulations were a driving force.
ETOPS regulations – or Extended-range Twin-engine Operational Performance Standards, first took
form as something 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. If one engine failed, there would be enough time to make
an emergency landing at the nearest airport using the other engine. As is obvious by the
name of the first such rule, the initial time was set at 60 minutes.
In the 1950s, the 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. 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, the 60-minute rule was waived for three-engined aircraft which opened the door
for manufacturers to develop widebody, intercontinental tri-jets, 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. 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 high fuel consumption of quad-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.
For the same reason carriers made shifts from four-engined aircraft towards three-engined
aircraft, airlines also shifted from three-engines to two: lower purchasing and operating costs
and greater efficiency. 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. This is why the Boeing 777 has become
one of the most popular widebodies ever with over 2000 orders to date.
So now that tri-jets are gone from the commercial passenger service, are we missing anything?
For the most part, no. Twin-jets offer the same levels of comfort, performance and, with
new technologies this keeps getting better. However, a key value of tri-jets or quad-jets,
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.
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.