There is nothing in the manual on how to recover an airliner using only engines to control it. So why not write it in? NASA wants to
NASA and the US Department of Homeland Security are investigating the feasibility of developing guidelines for ordinary airline pilots to help them to control an aircraft using throttles only. Potential loss of all hydraulic systems in the event of a missile strike is the motive, and the threat from man-portable air defence systems (Manpads) - shoulder-launched missiles - is reckoned to be sufficiently real to make the trial worthwhile.
NASA is using a Boeing 757 to start with, but in due course the team intends to produce individual guidelines for all the commonly used twinjets, taking into account their unique flying characteristics. At Baghdad in November 2003 the crew of a European Air Transport/DHL Airbus A300B4 saw their aircraft's left wingtip set on fire by a missile, and all hydraulic systems drained in seconds. But they lived to tell the tale when they successfully carried out a throttles-only recovery to land. So, however unlikely, the risk is there, and recovery is possible.
It doesn't always take a missile to do the damage. The crew of a United Airlines McDonnell Douglas DC-10 had to deal with a total hydraulic system loss in 1989 when its tail-mounted engine suffered catastrophic failure. The crew managed to guide the aircraft to ground at Sioux City, using just the two underwing engines. Not everyone survived the crash-landing, but the flightcrew and more than half the people on board did.
Eventually, if NASA has its way, pilots of all the in-service types may have a page added to their emergency checklist. But is it worth it?
Talking to Flight International a year after the Baghdad incident, the stricken A300's flight engineer Mario Rofail observed: "Situations like this are unique every time. You cannot train for them. You cannot write a checklist for them." Maybe NASA will prove him wrong. But maybe not. If an aeroplane takes a missile hit that drains its hydraulics, the situation may well be unique because the structural damage the aircraft has suffered will vary each time.
But producing throttles-only control guidelines for pilots may save lives, because the task is delicate and difficult. Every change of power when handling an aircraft using throttles-only control produces non-intuitive secondary and tertiary effects that cannot be countered with trim, stick or rudder, and the desired reaction to power changes is slow to develop. The only speed band available for controlled flight may be within a few knots of the airspeed the aircraft was trimmed to when the hydraulics drained from the horizontal stabiliser actuators. If the aircraft is on fire - as the A300 was - the crew may not have time to experiment with handling at altitude. A set of instant guidelines would be invaluable when there is little time in which to save the aircraft.
And before this point is forgotten, as the Sioux City and Baghdad events recede further into history, the pilots of the A300 and the DC-10 had an advantage: they had a flight engineer to help them. In any future event the pilots may well be on their own.
Source: Flight International
