Pilots familiar with stalls on transport-sized aircraft say an extended flight simulator envelope that Bihrle Applied Sciences has developed for the Boeing 737-800 closely mirrors aircraft performance during stall maneuvers, marking progress in the FAA's mandate to develop methods to improve stall training for pilots.

The agency plans to independently test the model this summer in advance of proposing new rules for enhanced simulators and training. Congress, as part of the 2010 Airline Safety Act, called on the FAA to begin providing ground and flight or simulator training to teach pilots to recover from stalls and upsets, a training deficiency noted in the 2009 Colgan Air Q400 loss-of-control crash near Buffalo, N.Y.

Simulators typically use extrapolated data outside of normal operating regimes, including in the stall and post-stall regimes, leading to aircraft responses that are benign and unrealistic. For that reason, simulators can only be used to train pilots how to recover the aircraft before a stall occurs. Accidents like Colgan, however, have revealed that pilots may not know how to recover an aircraft in the post-stall regime.

Jack Ralston, president of Bihrle Applied Research, says 737 pilots flying the company's extended envelope in a Sim Industries-built 737-800 full-flight simulator in Miami say the model is representative of 737-like aircraft. The simulator can be switched between extrapolated data and the extended data to highlight the differences.

Bihrle last year won a contract from the FAA to create a “representative” simulation model for a large transport aircraft to be used for stall training, but one that would not require flight test data in the stall and post-stall regime. That information can be too costly to obtain from airframers, assuming that it exists and they would be willing to provide it.

The FAA contract took advantage of tools developed as part of a U.S. Navy small business innovative research program to create extended models for the P-8A, a highly modified version of the 737-800.

Bihrle created the stall and post-stall nonlinear database using the aircraft's 3-D geometry, airfoil information and internal programs created during is 40-year history of collecting stall and wind tunnel test data, says Ralston.

FAA pilots sampled the 737-800 extended envelope in Miami in July 2012, and again in early February as part of an International Committee for Aviation Training in Extended Envelopes (Icatee) visit to the facility. Icatee, operating under the auspices of the International Civil Aviation Organization, is proposing that “representative” stall models may be adequate for stall training. A representative model does not exactly replicate a certain model of aircraft, but adequately mimics a set of jets with certain characteristics, for example a swept-wing widebody with one engine under each wing or an “envelope protected” aircraft like the Boeing 787 or Airbus A330. The FAA earlier this month issued a “broad agency announcement” in search of companies that may be able develop representative stall models that will properly reflect the performance of at least three different types of aircraft. Technical summary proposals are being accepted through May 31.

Along with the FAA pilots flying the simulator in February, Ralston says there were nine industry pilots, including some who have extensive experience recovering from stalls in the 737. “The response was extremely positive,” says Ralston. “The new model demonstrates the general lack of stability [in the post-stall regime] and requires appropriate response for recovery.”

Ralston says Bihrle created flight test cards and evaluation forms as part of the Miami trials as a precursor to the FAA's study this summer, which will most likely include test pilots as well as airline pilots flying the FAA's 737-800 simulator in Oklahoma City.