…And Sensitive Points About Sensitivity…


In his report, Hess notes that the “pedal/rudder sensitivity of the A300-600 at the airspeed at which the AA 587 accident occurred is the highest of all comparative transport aircraft.” For example, compared to the Boeing 767, the A300-600 pedal/rudder sensitivity is seven times greater, and it is 10 times greater than the preceding models in the Airbus series, the A300-600B2 and B4, Hess reports. “The sensitive nature of the rudder/pedal system is a plausible candidate for a control system property conducive to a PIO,” the report says. “One has a very powerful aerodynamic surface … activated by one of the most powerful muscles in the human body, commanding a pedal/rudder system that is considerably more sensitive than that of any comparable aircraft,” the report says. The report is still under consideration by the NTSB. “It’s [Hess’s] opinion. It’s not the board’s opinion at this point,” NTSB spokesman Ted Lopatkiewicz told Reuters last week. Hess elaborates that rudder pedals are operated by a pilot’s strong leg muscles — capable of exerting over 400 pounds of force — and he says those muscles lack the sensitivity to accurately command relatively small forces.

A response from the French Air Accident Investigation Bureau (BEA) questions Hess’s conclusions. The BEA disagrees with some of Hess’s assertions and says some of his data is inadequate. The Hess report does, however, “provide a springboard for questions that may lead to an understanding of this event,” the BEA concludes. Airbus officials also have defended the rudder system, noting that Airbus models have flown for millions of hours without rudder pressure being an issue. The NTSB’s final report is expected this spring.