My Boeing 737 flight from Stockholm with SAS is descending to Copenhagen. But
there’s something different. The engines are quieter, and with good reason:
they are idle. “We are effectively gliding into land,” says Captain Mathias
Wiberg as we pass over the spectacular Oresund Bridge that links Sweden with
Denmark. So, no thrust from the two engines, just a noiseless and
continuous, controlled descent from 20,000ft. At 500ft, Wiberg pushes the
engine into action and we continue to what is the smoothest landing I’ve had
in 30 years of flying.
This may have had something to do with the fact the flight took place in a
simulator at the Stockholm base for the Oxford Aviation Academy, a leading
global pilot training centre. With the concept of aircraft routinely flying
on non-fossil fuels still decades away, SAS and the academy are working out
ways to improve fuel efficiency dramatically.
By placing the engines in idle thrust mode (they are not actually switched
off), pilots reduce the amount of kerosene required by allowing the aircraft
to descend smoothly, rather than the step-by-step approach – with which most
readers will be familiar – and which, like a car continually changing gear,
uses up more fuel.
Several other measures contribute to what SAS describes as its “green
landings” programme. The energy efficient simulator flight began by taxiing
to the runway on one engine rather than two, the aircraft wobbling like a
supermarket trolley. Then we took off with almost no extended wing flaps and
accelerated to the normal cruise speed faster than usual, and at a
perceptibly higher angle – 11 degrees compared to eight degrees – and
immediately tucking away flaps and landing gear.
“With a higher take-off speed you get optimum performance,” explained Wiberg,
who selected several further fuel-saving options: an alternate airport
closer to the destination; a lower cruising speed; and a landing with a
similarly minimal and slightly disconcerting use of flaps, allowing the
friction of the runway to slow the aircraft, rather than lurching the
engines into reverse thrust.
The fuel saving was 17.5 per cent compared to a conventional flight, though
the variables of weather and air traffic control congestion mean the average
reduction since SAS launched the programme is closer to 4 per cent (with a
typical carbon saving of 60kg-80kg of carbon per flight).
SAS and the aviation industry argue none of these procedures compromises
safety. “We haven’t struck anything from the safety manual,” said Wiberg,
explaining that flight manuals give vast margins for error and safety. “You
are following the book, but you don’t need all these extra margins to feel