1st transatlantic green flight: close to 6 tonnes less CO2
Saturday 10, April 2010
This week, sustainable development week, Air France operated the very first transatlantic green flight, during which all procedures – from taxiing to arrival at the parking stand – were optimized to reduce noise and gas emissions. The 9 hour and 30-minute flight from Paris to Miami on 6 April was operated by a Boeing 747-400ER, with 436 passengers and 18 crew members on board.
The aircraft pushed back at 9:34 a.m. and took off from runway 09R. It taxied to the runway using just two engines (1 each side of the aircraft) out of 4 and the two others were started up at 9:48 by the crew who knew, in coordination with the control tower at Paris-Charles de Gaulle, that they would take off 5 minutes later, at 9:54 a.m.
The aircraft then climbed continuously, with no levels, thanks to excellent coordination between the control centres at Paris-CDG, Paris and Brest to reach an optimum cruising altitude of 33,100 feet (approximately 11,000 metres), given the flight conditions.
Contact was made as soon as possible with the control centre at Shanwick, which cleared the aircraft to fly between levels 330 and 350, i.e. between approximately 33,000 and 35,000 feet and at a speed of between 890 and 920 km/h.
The aircraft then started its cruise climb: the aircraft climbed 100 feet every 7 minutes to continuously correspond to the optimum altitude.
In this way, the transition between the control centres at Shanwick and Santa Maria in the Azores was made at the optimum altitude of 34,900 feet.
The control centre at Santa Maria then gave the following clearance:
“CRUISE CLIMB TO FL360 /REPORT LEAVING FL350/REPORT LEVEL 360” which enabled the aircraft to continue its cruise climb to level 360, i.e. close to 36,000 feet.
This level was almost reached when the flight was about to enter the U.S. controlled area at New York which cleared the aircraft to continue its cruise climb to a cruising altitude of 38,000 and then 39,000 feet. A simple calculation rule applies: to fly at an optimum cruising altitude, a Boeing 747 has to climb 747 feet every hour!
About half an hour before arrival at the Miami control centre, the crew of the aircraft made contact to plan its descent. Descent was continuous, from the optimum cruise altitude to landing, with only two radio exchanges with air traffic control which authorized descent to 14,000 feet, then an instrument approach to runway 09 at Miami airport.
After touchdown, the aircraft was cleared to taxi to the end of the runway and go straight to the parking gate, reducing taxiing to a minimum.
On arrival, thanks to the optimization of all these procedures, the crew was able to reduce fuel consumption by 2 to 3% and hence also reduce CO2 emissions.
Why does the aircraft continually have to gain altitude during the cruising phase to reduce consumption?
During a flight, we imagine that the cruise phase, between the ascent and descent, is "flat" and at a fixed altitude.
However, if we consider the optimal performance of an aircraft, this is actually quite different. For each aircraft, because of its aerodynamics and its engine type, there is an altitude known as the "optimum" altitude when the fuel consumption for a given distance is lower.
According to the principles of physics, the lighter the aircraft, the higher the optimum altitude. However, as the flight continues, the aircraft becomes lighter due to fuel consumption and the optimum altitude increases. The aircraft therefore has to climb regularly in order to consume less fuel.
--> 1,000 feet is approximately equivalent to 305 metres
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