Understanding the Stall-Recovery Procedure for Turboprop

Flight Safety DIGEST APRIL 2005 Understanding the Stall-recovery Procedure For Turboprop Airplanes In Icing Conditions Flight Safety Digest Flight Safety Foundation For Everyone Concerned With the Safety of Flight Vol. 24 No. 4 April 2005 www.fl ightsafety.org OFFICERS AND STAFF Chairman, Board of Governors Amb. Edward W. Stimpson President and CEO Stuart Matthews In This Issue Executive Vice President Robert H. Vandel General Counsel and Secretary Kenneth P. Quinn, Esq. Treasurer David J. Barger Understanding the Stall-recovery Procedure for Turboprop Airplanes in ADMINISTRATIVE Icing Conditions Manager, Support Services Linda Crowley Horger Current pilot training typically emphasizes powering through a FINANCIAL stall recovery with no loss of altitude. Nevertheless, when fl ying a turboprop airplane that has accumulated ice, lowering the Director of Finance nose to reduce angle-of-attack is imperative. Here’s why. and Administration Juan G. Gonzalez Accountant Millicent Wheeler 1 MEMBERSHIP No Fatal Accidents Disrupted Director, Membership STATS and Development Ann Hill Australian Regular Public Transport, Membership Services Charter Operations in 2004 Coordinator Ahlam Wahdan Accident rates for regular public transport and fatal-accident PUBLICATIONS rates for charter operations have trended lower over a multi-year period. No comparable trend, however, can be seen in fatal- 18 Director of Publications Roger Rozelle accident rates for private/business operations. Senior Editor Mark Lacagnina Senior Editor Wayne Rosenkrans Senior Editor Linda Werfelman ‘Socio-technical Failures’ Associate Editor Rick Darby Called a Safety Threat Web and Print Production Coordinator Karen K. Ehrlich Models of human error derived from engineering and Production Designer Ann L. Mullikin LIBRARY experimental psychology are inadequate to understand Production Specialist Susan D. Reed the complex interaction among technology, operators and organizational systems, the author says. Librarian, Jerry Lederer 22 Aviation Safety Library Patricia Setze TECHNICAL B-767 Encounters Hail, Director of Technical Programs James M. Burin Wind Shear During Takeoff 27 Technical Programs Specialist Joanne Anderson The report by the Australian Transport Safety Bureau said Managing Director of that neither weather forecasters nor air traffi c controllers Internal Evaluation Programs Louis A. Sorrentino III BRIEFS had a complete picture of the deteriorating weather Q-Star Program Administrator Robert Feeler conditions at the departure airport. Manager, Data Systems and Analysis Robert Dodd, Ph.D. Manager of Aviation Safety Audits Darol V. Holsman Founder Jerome Lederer 1902–2004 Flight Safety Foundation is an international membership organization dedicated to the continuous improvement of aviation safety. Nonprofi t and independent, the Foundation was launched offi cially in 1947 in response to the aviation industry’s need for a neutral clearinghouse to disseminate objective safety information, and for a credible and knowl- edgeable body that would identify threats to safety, analyze the problems and recommend practical solutions to them. Since its beginning, the Foundation has acted in the public interest to produce positive infl uence on aviation safety. Today, the Foundation provides leadership to more than 900 member organizations in more than 150 countries. Cover photo: © Copyright 2005 Getty images Inc. Supercooled large droplets froze instantly on contact with a side window in the airplane cockpit during an icing test flight. (Source: John P. Dow Sr.) Understanding the Stall-recovery Procedure for Turboprop Airplanes in Icing Conditions Current pilot training typically emphasizes powering through a stall recovery with no loss of altitude. Nevertheless, when flying a turboprop airplane that has accumulated ice, lowering the nose to reduce angle-of-attack is imperative. Here’s why. — JOHN P. DOW SR. ost encounters with icing condi- required for stall recovery will better prepare tions in turbopropeller-driven a turboprop airplane pilot to respond to one (turboprop) airplanes are rela- of these infrequent but very dangerous icing Mtively benign and demand little encounters. more than promptly activating the airplane’s ice- protection systems and finding an ice-free alti- An airplane upset is defined by the Airplane tude. Nevertheless, there have been encounters Upset Recovery Training Aid as including the fol- with icing conditions that have caused rapid and lowing unintentional conditions: “Pitch attitude adverse airplane responses, including stalls that greater than 25 degrees nose-up; pitch attitude have led to airplane upsets and loss of control. greater than 10 degrees nose-down; bank angle A broader understanding of what might be greater than 45 degrees [or] within the above FLIGHT SAFETY FOUNDATION • FLIGHT SAFETY DIGEST • APRIL 2005 1 U NDERSTANDING THE STALL- RECOVERY PROCEDURE parameters but flying at airspeeds The researchers said that a primary factor in suc- inappropriate for the conditions.”1 cessful recovery was nose-down elevator input. The training aid says that specific Their report said: values may vary among airplane models. The pilots appeared to respond in accordance with their training for excessive bank and stall Loss of control is defined by the recovery, but they did not implement corrective European Joint Aviation Authorities actions uniquely required for icing-induced roll (JAA) Safety Strategy Initiative as “a and uncommanded control movement. These situation in which the crew fail[s] two types of recoveries require different respons- to maintain/regain control of an es: Normal stall-recovery training (which trains aircraft. This can result from external pilots in recovering from the approach to stall) factors, such as icing or mechanical emphasizes applying maximum power and failures.”2 minimizing loss of altitude. In contrast, recovery from icing-induced rolls and more complete The U.S. Commercial Aviation stalls requires trading altitude for airspeed. Safety Team has a similar, but broader, defi nition: “Loss of control refers to accidents resulting Fly Like You Train (Usually) from situations in which the pilot should have maintained or regained aircraft ost ice-related stalls and upsets occur in in- control but did not.”3 Mstrument meteorological conditions (IMC). Instrument interpretation (e.g., when the airplane Examination of digital flight data recorder is in an unusual attitude) requires skills that pilots (DFDR) data from turboprop airplanes involved typically have not developed in training or from in ice-related loss-of-control accidents has shown experience. Moreover, because an ice-related stall some common characteristics. For example, in typically occurs at a lower-than-normal AOA three fatal accidents that resulted in 134 total (and higher-than-normal airspeed), the stall can fatalities, the pilots initially did not reduce wing surprise the pilot. angle-of-attack (AOA) by moving the control column to the nose-down position early in the Pilots of turbine airplanes typically are trained in upset sequence. The accidents involved an Avions fl ight simulators to respond to the fi rst indication de Transport Regional ATR 42 in Crezzo, Italy, of a stall by applying power and maintaining pitch in 1987;4 an ATR 72 in Roselawn, Indiana, U.S. attitude, with the objective of losing no altitude in 1994;5 and an Embraer Brasilia in Monroe, during recovery. Thus, in theory, the airplane Michigan, U.S., in 1997.6 will accelerate to an increased airspeed and a reduced AOA. The procedure results in recovery The DFDR data from the three accident airplanes in the simulator; nevertheless, the procedure will show that AOA either remained close to the angle not always result in recovery in an airplane with at which airfl ow separation occurred or that AOA fl ight characteristics degraded by ice. increased, compounding the severity of the upset and making recovery more diffi cult and unlikely. The training follows U.S. Federal Aviation Other ice-related incidents from which fl ight data Administration (FAA) practical test standards were available also involved AOAs that were main- (PTS). The PTS for the private pilot certifi cate tained or increased. and the PTS for the commercial pilot certifi cate, for example, specify a “minimum loss of altitude” The scenario that was involved in the Roselawn during stall recovery. accident was duplicated in a flight simulator during a study conducted for the U.S. The PTS for the airline transport pilot certifi cate National Aeronautics and Space Administration and for aircraft type ratings require recovery to (NASA).7 The subjects for the study were 40 be initiated at “the fi rst indication of an impend- newly hired airline pilots; fewer than half were ing stall” and to be completed with “acceptable” able to recover. altitude loss. The JAA standards are similar. 2 FLIGHT SAFETY FOUNDATION • FLIGHT SAFETY DIGEST • APRIL 2005 U NDERSTANDING THE STALL- RECOVERY PROCEDURE AFM Procedures Vary Nevertheless, the PTS standards — primarily those for the ATP certifi cate and airplane type ratings ome airplane fl ight manuals (AFMs) and fl ight — typically are adhered to during training. Screw operating manuals (FCOMs) include rec- ommended stall-recovery procedures, although “It doesn’t make much difference what the the information is not required. The FCOMs for manufacturers recommend, the pilots that fl y the ATR 42 and the ATR 72, for example, recom- the airplanes must get a check ride from the FAA mend the following procedure

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