Which Aircraft Can Carry An Extra Engine On Their Wings?

It’s a rare sight in the skies but a hypothetical possibility: A Boeing 747 flying with five engines. Last year we discussed how Qantas did this in 2016 as a way of ferrying a spare engine to one of its jumbo jets stranded far from home. But are there any other aircraft capable of doing something similar?

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In 2016, Qantas flew one of its 747-400s to Johannesburg, South Africa. A Qantas 747 there needed a replacement engine and this method of transport was the best option for the airline.  Photo: Qantas

The Queen of the Skies: Built to carry extra engines

Right from the beginning, the Boeing 747 was designed with the ability to carry an extra engine under its wings. In fact, it wasn’t just Qantas that has done this. Although the airline is perhaps one of the most recent examples with its 2016 incident, prior to this, it also noted a similar experience in 2011.

But if you look hard enough, you’ll find old photos of various airlines having done the exact same thing over the decades: Ferry an extra engine under the wings of the Queen of the Skies.

Although we don’t know how frequently this occurred, we do know that it was being done by airlines all over the world. Indeed, airlines that we were able to find photos of include British Airways, its predecessor BOAC, Singapore Airlines, South African Airways, Aer Lingus, and TWA. Undoubtedly, there are more airlines out there that took advantage of this 747 feature.

So why did Boeing include this capability on its jumbo jet? Well, at the time, the size of the 747’s engines were too large to be transported within other aircraft. Additionally, time-consuming transportation by land and sea would have presented their own logistical challenges. As one of our YouTube viewers notes, having this 5th anchor point was very useful for aircraft maintenance and engine transport- particularly when an aircraft was “stranded” away from home base.

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Vickers VC-10

According to VC10.net, the designers of the Vickers VC10 gave it the ability to carry an extra engine under its wing. 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, with the chance of engine failure being more significant than it is today.

Vickers’ solution made it so that a pod could be attached to the wing root on the righthand side, which was capable of holding a spare Rolls-Royce Conway engine.

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The Vickers VC-10 could carry a spare engine under its wings. Photo: Ken Fielding via WIkimedia Commons 

The 707 and DC-8

While the 747 was built with the ability to transport an additional engine under its wing, it wasn’t the first aircraft to do so. Indeed, 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 notes:

“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 like it all began 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. The DC-8’s first flight was in 1958.

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A photo of a Qantas 707 flying with an additional engine. Photo: Qantas

Trijets becoming quadjets: The DC-10 and L1011

While newer designs than the previously mentioned jets, two 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.

What about Airbus quadjets?

Given that an extra engine could be mounted under the wings of the 707 and 747, you might be led to ask “what about Airbus”? Well, as far as we can tell, this was never a capability for the European planemaker’s A340 and A380 quadjets.

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(er) 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.

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