NTSB Studies GA Weather Accidents

Aviation International News » October 2005
October 24, 2006, 10:31 AM

Noting that about two-thirds of all general aviation accidents that occur in IMC are fatal, the NTSB recently completed a study to better understand the risk factors associated with such accidents.

The Board used “case control methodology,” which compared a group of accident flights to a matching group of nonaccident flights to identify patterns of variables that distinguished the two groups from each other.

The advantage of the case control methodology is that it identifies characteristics that set accidents apart and contribute to their occurrence rather than focusing on the factors that accidents have in common.

NTSB air safety investigators collected data from 72 GA accidents that occurred between August 2003 and April last year. When accidents occurred, study managers also contacted pilots of flights that were operating in the vicinity at the time of those accidents for information about their flight activity.

Safety Board Conclusions

Investigators included 135 non-accident flights in the study. All nonaccident pilots voluntarily consented to interviews and provided information about their flight, their aircraft and details about their training, experience and demographics. Investigators compared that information with data regional air safety investigators collected about the accident flights as part of their normal investigations. Additionally, the FAA provided information about pilots’ practical and written test results and their previous accident/incident involvement.

The Board concluded that:

• Pilots who start flying earlier in life are at lower risk of being involved in a weather-related GA accident than those who start flying when they are older, and age at first certificate is a better predictor of future accident involvement than age at time of flight.

• The observed connection between age and accident risk in this study is not likely the result of physical aging issues, but of other factors associated with the age at which a person starts flight training.

• Periodic training and evaluation may be necessary to ensure that pilots maintain weather-related knowledge and skills.

• Pilots who fail either a knowledge or practical test have a higher risk of being involved in a weather-related GA accident than pilots who pass those assessments.

• A pilot can answer all questions relating to weather on a knowledge test incorrectly and still receive a passing score on the test.

• A history of accident or incident involvement is associated with a higher risk of being involved in a weather-related GA accident.

• GA pilots routinely consult alternative sources of aviation weather to obtain information that is not currently available from a standard weather briefing.

The Board emphasized that the conclusions reached in this study are not based on a summary of accident cases. Rather, the results are based on a statistical comparison of accident and nonaccident flights that allows for the generalization of findings from this study to the wider population of GA pilots and flights that might be at risk for a weather-related accident.

As a result of the study, the NTSB recommended that the FAA add a specific requirement for all pilots who do not receive weather-related recurrent training that the biennial flight review (BFR) include recognition of critical weather situations from the ground and in flight, procurement and use of aeronautical weather reports and forecasts, determination of fuel requirements and planning for alternatives if the intended flight cannot be completed or delays encountered.

The safety agency also recommended that, for pilots holding a private, commercial or ATP certificate in the airplane category who do not receive recurrent instrument training, the FAA add a specific requirement that the BFR include a demonstration of control and maneuvering of an airplane solely by reference to instruments, including straight-and-level flight, constant-airspeed climbs and descents, turns to a heading and recovery from unusual attitudes.

The Safety Board urged the FAA to find the best way to convey FSS weather briefings–including the possibility of supplementing or replacing some portions of the current standard weather briefing with graphical data– and to provide guidance to pilots on using the Internet, satellite and other data sources for obtaining weather information suitable for meeting FAR preflight requirements.

The NTSB also suggested that the FAA establish a minimum number of weather-related questions that pilots must answer correctly to pass knowledge tests, identify pilots whose performance history indicates that they are at risk for accident involvement and develop a program to reduce risk for those pilots.

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