[عاشق A380]

FAA workgroup urges low-speed rejected takeoff guidance

An FAA-sponsored working group has recommended the US agency develop guidance requiring demonstrations that aircraft can be controlled when an engine suddenly loses thrust during the low-speed portion of a takeoff run, as well as training recommendations for pilots on how to respond to the rare but potentially tricky events.

The recommendations, made in a recently completed report from FAA’s Aviation Rulemaking Advisory Committee Flight Test Harmonization Working Group (FTHWG), stem from a 2010 incident in Sweden. An Iran Air Airbus A300-600 veered off the runway at Stockholm Arlanda Airport following a No. 1 engine failure as the aircraft approached 54 knots in its takeoff run. The initial veer occurred during a key 1.5-sec. span after the No. 1 engine failed and the No. 2 engine was at full power. Though the pilots reacted quickly—retarding the thrust levers, applying rudder and brakes, and attempting to steer the aircraft within 1 sec.—investigators found the Airbus widebody twin left the runway and continued 650 ft. off the runway surface, and 120 ft. laterally from the runway edge. All 170 passengers and crew evacuated safely in what the SHK, Sweden’s accident investigation authority, labeled a “serious incident.”

Several factors, including runway conditions the pilots were not adequately warned about and unintentional asymmetric breaking, likely contributed to the incident. But investigators also pointed to the rare combination of asymmetric thrust, such as when an engine fails, at speeds too slow to render control surfaces useful to counteract yawing. Mix in a contaminated surface—the Iran Air crew was told the runway condition “good with some patches of ice,” but investigators determined it was probably worse—and the incident uncovered a regulatory gap.

“There are no specific certification requirements for [an] aircraft design organization to show that the aircraft is maneuverable in the event of a sudden loss of engine thrust during the initial stage of the takeoff sequence,” SHK wrote in its final report. “There are also no mandatory requirements for training regarding how to handle sudden losses of engine thrust during the initial stage of the takeoff sequence for pilots in training or recurrent training for this class of aircraft.”

Among SHK’s recommendations to FAA and the European Aviation Safety Agency (EASA): consider requiring yaw-stability demonstrations for low-speed engine failures on takeoff, and ensure the scenario is covered in both initial and recurrent training.
EASA told SHK that current requirements in its Certification Specifications 25.143 for a minimum control speed on the ground are sufficient and noted that there is “low service history of this type of incident.” EASA said it continues to monitor the issue.

FAA in 2013 took a similar stance, citing the infrequency of these incidents. But the FTHWG subsequently took the issue up.

While FAA’s Part 25 regulations “assess the general aspects of controllability” during all phases of flight, including phase-transitions and engine failures, neither the rules nor supporting guidance specifically address low-speed, engine-out rejected takeoffs [RTO], the working group found.

The group’s study included modeling 20 simulation scenarios for different aircraft types to determine factors—such as wind speed and aircraft configuration—that could contribute to lateral deviation during a low-speed rejected takeoff. The scenarios also considered various flight-crew reactions, such as how fast brakes were applied.

Once it identified the riskiest combinations of factors—including wet or contaminated runways, crosswinds, widebody twin-engine aircraft and aft center-of-gravity-loaded configurations—the group set out to address the issue. The group decided that new requirements in the regulations, such as mandating automatic takeoff thrust control systems, could create more issues than they solve.

“It seems inappropriate with the current technology to mandate the implementation of systems such as those [discussed] (or to otherwise introduce controllability regulations that would inevitably lead to those systems). They would unduly increase the cost and complexity of new Part 25 aircraft and introduce additional sources of failures and combinations of failures,” the group explained. “The balance between the potential benefit and the unintended consequences is under par given the unlikely combination of” factors that create the most risk, it added.

The working group settled on recommending guidance “specifying a new Part 25 standard RTO demonstration by flight test or simulation on dry runway.” The guidance would be Incorporated into Advisory Circular 25-7, “Flight Test Guide For Certification Of Transport Category Airplanes.”

FAA also should consider ground training for low-speed RTO that raise awareness of certain issues, such as the risks certain weather conditions pose, and emphasize quick reactions.

The working group included representatives from manufacturers Airbus, Boeing, Bombardier, Dassault, Embraer, Gulfstream and Textron; regulators from Brazil, Canada, Europe, and the US; and the US Air Line Pilots Association.

https://atwonline.com/regulation/faa-...keoff-guidance