Safety Bureau calls for new line of defence in flight software

The Australian Transport Safety Bureau has called on software developers to incorporate "reasonability checks" into flight management systems to reduce the risk of aircraft take-off incidents like tail strikes.

The bureau has handed down a lengthy analysis of accidents and incidents worldwide that were caused by take-off performance data being incorrectly calculated or entered into aircraft systems.

Although acknowledging it wasn't a silver bullet to data entry errors by flight crews, the ATSB called on the makers of flight management systems to introduce more checks and balances into their software in a bid to pick up on human errors before they caused incidents.

The bureau said that the design of some systems "affected their usability and made it easier for crew errors to occur, or difficult to detect errors that did occur".

Problems the ATSB identified included lack of standardisation when it came to input values needed to calculate take-off speeds, "no inbuilt function to alert the user that the values entered were unrealistically low or mismatched" and performance software that, when opened, automatically reverted to information entered for the previous flight.

"When designing aircraft systems such as the flight management computer (FMC) or performance software on handheld performance and laptop computers, manufacturers and software developers should consider standardising input values and implementing reasonability checks where possible," the bureau recommended.

However, it did note warnings by Boeing that software enhancements of this type could be ineffective or result in an increase in "nuisance warnings" being generated.

The ATSB also sought some sort of systems integration where more than one system was
"available for calculating take-off performance parameters".

The bureau said that software should be able to warn flight crews if it identified a margin of error between what it and other flight computers were showing.

The report noted a range of systems and devices were involved in calculation errors. Some were manual but many involved laptops, handheld computers, flight computers and communications systems.

"As technology evolves, machines become more complex, which in turn affects the way in which humans and machines interrelate," the ATSB stated.

"This interaction has created a new set of error modes."

Typical errors included miscalculations of the aircraft's zero fuel weight (defined as the total weight of the aircraft, including the pilots, cabin crew, passengers, baggage, cargo, food and water, but excluding the useable fuel) its take-off weight (the total weight of the aircraft at the time of takeoff), plus transcription and data entry mistakes.