NASA has developed and patented a simplified version of a propulsion controlled aircraft (PCA) system enabling pilots to land even if aircraft control surfaces are out of action. Known as PCA Lite, the new system does not require software changes to be made to the aircraft's engines.
The invention builds on the original PCA system developed following the July 1989 United Airlines McDonnell Douglas DC-10 crash in Sioux City, Iowa, due to loss of hydraulic system power. The PCA system allows the aircraft to manoeuvre and land using precise control of engine power alone, and was tested successfully on an MD-11 in 1995.
John Burken, one of the NASA Dryden engineers who developed the simplified PCA, describes it as a "poor man's version" of the original concept. NASA says the simpler system combines a 5% engine pressure ratio (EPR) trim feature with the aircraft's autothrottle pitch mode. "By using the existing 5% limits, the engine computers allow for yaw/roll to be intentionally improperly trimmed," says the agency. The commands going to the full authority digital engine control (FADEC) for the mistrim can be used for aircraft control. "Therefore," says NASA, "...no modifications to jet engine computers are needed."
This overcomes a key hurdle in the form of engine manufacturer warranties which appears to have prevented widespread adoption of the PCA. These are voided if the engine is modified, as was the case with the original PCA system.
NASA says another advantage of the "Lite" version is that it uses existing autothrottle systems for pitch control, rather than requiring the development and certification of another flightdeck control. Under PCA control, the autothrottle would increase thrust to climb the aircraft, or vice-versa to cause it to descend.
Source: Flight International