As passenger numbers fall during the global economic slump, airlines are increasingly downsizing to Boeing’s 777 on long-haul routes.

The 777, or “triple seven” as it is known, is taking over from the 747 jumbo jet on many routes because its lower seating capacity and fewer number of engines make it more economical to fly.

The aircraft is becoming the workhorse of long-haul travel and airlines such as British Airways are relying on it more and more. For example, when BA decided recently that it needed to add new aircraft to its fleet quickly it selected the 777. It will take delivery of six more in the next two years, taking its 777 fleet to 45.

The 777 entered service in 1995 and Boeing has so far delivered 763 with a further 338 on order. At up to $250 million each, the 777 has generated revenues of nearly $275 billion for Boeing. The aircraft has been a massive commercial success and Boeing jealously guards its reputation.

So the recommendation from the National Transportation Safety Board (NTSB) in America that urgent changes are required on its engines will be causing extreme concern in Seattle, the 777’s home.

The aircraft’s popularity with airlines has been built on its ability to carry large numbers of passengers a very long distance on only two engines. The 747 and Airbus’s A380 both have four engines, which allow a greater take-off weight but burn more fuel.

On many routes, such as Heathrow to New York or Los Angeles, there are sufficient passengers to justify airlines operating big and heavy 747s and A380s.

However, on nontrunk routes the 777 makes more economic sense. This is particularly true when passenger numbers are falling as carrying empty seats halfway around the world is incredibly wasteful and expensive. The twin-aisle 777-200 typically carries about 300 passengers in a three-class configuration while its bigger sibling, the 777-300, carries about 365. This compares with 416 in a modern 747 – only 14 per cent more passengers but at least 20 per cent higher fuel consumption.

The 777’s lighter body gives it the longest range of any commercial aircraft in the world and four years ago a 777-200LR (long-range) set a new distance record of 11,664 nautical miles (21,601 kilometres). The aircraft left Hong Kong and flew east, crossing the Pacific, North America and then the Atlantic before landing at Heathrow 22 hours later.

Passengers getting on ultra-long-haul journeys of 13 or 14 hours’ duration can therefore expect to be on a 777 or Airbus’s rival A330 and A340.

To enable these aircraft to make journeys of such length, Boeing has equipped the 777 with the largest turbo-fan engines in the world. The General Electric 90-115Bs on the 777-300ER (extended range) are like having a double-decker bus hanging under both wing. These engines are so big that their diameter is actually wider than the fuselage of the 737, the aircraft operated by carriers such as Ryanair.

Rolls-Royce also offers airlines its Trent engine for the 777 and the British company has about one quarter of the market. It is the Rolls engines that have sparked the NTSB’s concern and the company will be working closely with Boeing to resolve the issue before any more aircraft have a problem.

For Boeing this is incredibly important as there have been no 777 fatalities so far and only a few “incidents”, such as the crash-landing of BA’s Beijing to Heathrow flight in January 2008 and a thrust failure on a Delta flight in November.

The cause of both incidents is thought to be ice forming in the fuel lines, and Rolls and Boeing will be examining how this occurs.

This is a bigger issue for the 777 than nearly any other aircraft type as its very long range allows airlines to fly over the poles, connecting cities such as Singapore with New York – routes that would not be viable if flown around the globe.

The question Boeing and Rolls must consider is whether the cold temperatures on these routes directly causes the icing because of a design flaw in the engine. If this is the case, the Rolls-powered 777s will have to be grounded until the problem is resolved, as the risks are simply too great to keep them flying.

The 777 is an outstanding piece of engineering and does not deserve to have its reputation tarnished by such an accident.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive