Sat Mar 31, 2001 12:48 pm
From the December, 2000 issue of Airways pg. 32-43.
The aircraft was a South African 747-400 powered by RR RB211-524H engines with 60,600 lbs. of thrust each. The flight was SAA Flight 202 from JFK to Johannesburg. 14 hr. 35 min. flying time (it's a extremely long flight).
Avg. wind component of +12 knots, planned flying time of 13 hr. 56 min., and a planned landing with 23,540 lbs. of fuel.
From pg. 33
Like many old heads, Erasmus does not always agree with the computer prognostications. He selected Mach 0.86 for cruise. The computer selected 0.855 for long-range cruise and 0.847 for best economy. Capt Erasmus says, "At .86 we will burn more fuel initially but overall I can usually beat the flight plan." With an en route time of 13:56 and a burn of 156,820lb this works out to 24,700lb/hr, slightly higher than the captain's estimate. However, if you take out the 5% penalty, the figures are very close. At the end of the flight we will see how it worked out.
From pg. 34
Our fuel remaining "in the blocks" was 23,590lb for a burn-off of 353,180lb, including taxi. Flight plan would have been 351,196lb burn-off with taxi. However, at the lower planned Mach 0.84-0.85, the trip would have lasted longer. More fuel would have been used. So it looks like Capt Erasmsu was right on this trip.
To sum it up, the writer is saying that cruising faster shortened the trip, so even though the fuel burn was higher per hour, the overall time lessened the trip enough that it was more efficient to go faster.