Why Did Tri-Jet Passenger Planes Not Become Popular? [2/6] - Increasingly efficient and reliable twin-jets have reduced the need and demand for aircraft with more engines.png (1/1)

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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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