DR. Dr!, as promised, having had an amenable Flight Planner for our flight on Thursday, he kindly ran through the Big Airways flight planning computer comparison figures for a New York flight limited to 24,000' as compared to the standard altitude requirement. This was for a B747-400 on 07 Aug 2003. The common figures are:
Zero Fuel Weight 220,000 kgs
Payload 31,700 kgs
Planned Fuel remaining at Destination 10,700 kgs
Standard
Step climbs at approximatel quarter points 34,000', 36,000' and 38,000'
Fuel required to destination 62,739 kgs and time 06.48
Altitude Restricted
Limited to 24,000'
Fuel required to destination 72,616(*) and time 06.44
(*) Note. The flight planner was unable to prevent the computer desperately wanting to climb once the Oceanic leg was completed. At 1.45 hrs from New York, the computer assumed a climb in the remaining time to 40,000' to try and save a bit of fuel, so the actual 'all the way figure at 24,000' would have been several hundred kgs higher.
Thus limiting cruise to 24,000' all the way would have consumed more than 10,000kgs extra fuel on top of the 62,739 actually used through a high level cruise. What surprised me was the time factor- actually slightly quicker at 24,000'. The burning question of the day, therefore, is:
"Is it better to reduce contrail pollution by burning an extra 16% (approx) fuel and producing that much extra exhaust pollution?"
Another relevant point- high altitude air is not floating around up there forever- like on surface meteorological charts, it moves horizontally. Over surface high pressure areas, the air subsides from high altitude (thus creating poor visibility hazy conditions that doesn't clear easily as particles are not removed from near the surface), over low pressure areas, air rises, clearing the atmosphere but producing cooling condensation into cloud. Therefore the minute amount of water injected into the atmosphere will eventually find its way back into the water cycle. I'm afraid this research team have been bending facts to make it fit their hypothesis!
Now Dr., about me back.............