aircraft: an AG330 starter cart with two Buick V8 engines driving a common output shaft, or compressed air driving a small starter adapter. The air-start method superseded the cumbersome "Buicks" when better compressed air supplies became available. Fuel Any aircraft flying at three times the speed of sound is in a severe thermal environment, both from frictional heating and stagnation ram rise. The fuel was the only heat sink available to the aircraft and after absorbing , keeping everything cool enough from the crew to the exhaust nozzle area indicator, it was supplied to the fuel nozzles at . To cope with these high temperatures, a new jet fuel with a low vapor pressure had to be developed. A chemical method for igniting the fuel, triethyl borane (TEB), was developed to match its low volatility. TEB spontaneously ignites in contact with air above −5 °C. The engine and afterburner were lit with TEB and the afterburner also had a catalytic igniter that glowed in the hot turbine exhaust. Each engine carried a nitrogen-pressurized sealed tank with of TEB, sufficient for at least 16 starts, restarts, or afterburner lights; this number was one of the limiting factors of SR-71 endurance, as after each air refueling the afterburners had to be reignited. When the pilot moved the throttle from cut-off to idle position, fuel flowed into the engine, and shortly afterwards an approx. shot of TEB was injected into the combustion chamber, where it spontaneously ignited and lit the fuel with a green flash. In some conditions, however, the TEB flow was obstructed by coking deposits on the injector nozzle, hindering restart attempts. Refilling the TEB tank was a perilous task; the maintenance crew wore silver fire suits. Conversely, the JP-7 fueling was so safe that some aircraft maintenance was permitted during filling. The chemical ignition was chosen instead of a conventional igniter for reliability reasons, and to reduce mechanical complexity. The TEB tank is cooled with fuel flowing around it, and contains a disk that ruptures in case of overpressure, allowing TEB and nitrogen to discharge into the afterburner. One heat source required two-stage reduction. Before entering the fuel heat-sink system, the Environmental Control System (ECS) air leaving the engine compressor at was so hot that ram air at had to be used first. Fuel flowing from the tanks to the engines was used to cool the air conditioning systems, aircraft