It’s a rare sight in the skies but technically still a possibility:
A Boeing 747 flying with five engines. We’ve discussed before how Qantas did
this in 2016 as a way of ferrying a spare engine to one of its stranded jumbo jets.
But are there any other aircraft capable of doing something similar?
Right from the beginning, the Boeing 747 was designed with the ability to carry an extra engine
under its wings. Although Qantas’ 2016 incident is perhaps one of the most recent examples,
it also did the same in 2011. Although we don’t know how
frequently this occurred throughout 747 operations, we do know through photographic
evidence that ferrying an extra engine was done by airlines all over the world.
So what other aircraft had this capability? Well, according to VC10.net, the designers
of the Vickers VC10 gave it the ability to carry an extra engine under its wing too.
The aircraft is powered by four engines mounted at the rear, thus providing ample space under
the wing to transport a spare powerplant. This was made all the more important due to the lower
levels of jet engine reliability at the time. Vickers’ solution saw a pod attached to the wing
root on the righthand side, which was capable of holding a spare Rolls-Royce Conway engine.
Before the 747, the Boeing 707 was among the first to take a fifth engine under the
wing – even if it wasn’t something that Boeing originally thought of with the quadjet’s design.
On its website, the Qantas states: “We first pioneered the carriage of a
fifth engine with our Boeing 707s back at the dawn of the jet age to save shipping costs.”
So, if we take Qantas at its word (the main word being ‘pioneer’),
then it sounds things started with the Australian airline and its Boeing 707s.
The carrier took delivery of its first 707 in 1959.
However, in message threads covering the presence of additional pods for ferrying
engines, there is discussion that the Douglas DC-8 also had this ability.
This type had its first flight was in 1958. Two newer trijets- the McDonnell Douglas DC-10
and Lockheed L1011 – were also designed with the ability to carry an extra engine.
In the case of the DC-10, the extra engine would be transported with a special nose cone that would
cover the whole engine intake and additional cowls/fairings. This gave the engine somewhat of
an egg shape. Additionally, the extension range of the inboard slats had to be reduced to avoid
impact with the spare. The horizontal stabilizer’s take-off warning range was also altered.
So why doesn’t the practice of ferrying a spare engine under the wing happen anymore?
Well, as a contributor on Stack Exchange notes, “one of the main reasons the 747 was
given the ability to ferry an engine was due to the lack of large cargo aircraft available
at the time.” The 747 itself pushed the limits of how big a commercial aircraft could be.
Thus, it wasn’t until Boeing offered a freighter variant of the 747 that large engines could be
transported within the main holds of aircraft. Since those early 747 days, cargo aircraft have
become more ubiquitous, with freighter variants ranging from the small 737
all the way up to the 747-8 and, of course, the mighty Antonov An225. As a result, newer jets
and their larger, high bypass turbofan engines could have their spare powerplants transported
in a variety of purpose-built freighters. Did you know about these various aircraft
and their ability to carry an extra engine? Let us know in the comments.