Miloch wrote in
:

https://simpleflying.com/tri-jet-pas...s-not-popular/

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, SWISS, 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.



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