It takes considerable effort on our part, but BCA's annual Purchase Planning Handbook (May issue) has become one of the most trusted specifications and performance references for business aircraft extant. The handbook is regularly used to gauge the capabilities of business aircraft during pre-purchase negotiations because multi-million-dollar investment decisions frequently hang in the balance. PPH readers have confidence that aircraft in the listings will perform up to published expectations.
They know, for instance, that when the PPH shows that a specific large-cabin business jet can carry eight passengers with full fuel, fly 6,500 nm and then land with 200-nm IFR reserves, it will do so.
But those capabilities are subject to several assumptions set forth by the NBAA, and not us; these include:
Actual aircraft basic operating weight must not be greater than the published weight.
The instrument departure procedure at the origin airport follows the great circle path directly to the destination airport.
ATC authorizes an unrestricted climb to the ideal cruise altitude.
Outside air temperature is no warmer than standard day conditions.
The landing arrival and instrument approach procedures overlay the tail end of the great circle route to the destination airport.
Are the calculations correct and meaningful?
“Sure. If you can fly a perfect flight test profile, then you can make the numbers,” says Robert Agostino, former head offlight operations. “You have to assume there are no other aircraft [flying] on the planet. You cannot be held down by ATC. You have to assume winds aloft no stronger than 75% or 85% historical averages and ISA-day temperatures.”
A typical NBAA IFR range assumes just such an ideal flight profile. Ten minutes are allocated for start and taxi at idle thrust at the departure airport, and 1 min. for takeoff at full thrust. The crew gets ATC clearance for an unrestricted climb on course to the ideal initial cruise altitude. ATC gives two additional step-climbs at the ideal points in the flight profile. The aircraft remains at altitude until the optimal descent point and then ATC clears the crew for a continuous 3,000-fpm plunge to a slam-dunk, straight-in instrument approach with fuel burn equal to 5 min. of loiter time at 5,000 ft.
For the missed approach at the destination and the 200-nm divert to an alternate airport, the NBAA assumes a direct climb to 5,000 ft. and 5 min. of loiter time to receive the route clearance to the alternate. En route to the alternate, the range format assumes an ideal climb, cruise and descent profile. The aircraft lands with a 30-min. VFR fuel reserve.
Such assumptions have led to a decades-long disconnect between aircraft marketers, who use the NBAA-range figure as a comparator, and operators, who rely instead on their ops manuals and practical experience.
Agostino notes, “If any of my crews actually were to land with only 30 min. of fuel in the tanks, that situation would be grounds for a very serious discussion with the head of the flight department.”
In other words, the crew quickly would be seeking other employment opportunities, absent their presenting clear and convincing evidence that they couldn't have foreseen delays and other factors that caused them to run so short on fuel reserves.
Agostino has equally clear and direct communications with his passengers. As a result, they understand that real-world operating conditions can reduce the theoretical NBAA IFR range of an aircraft by 10 to 20%, or more.