The Federal Aviation Administration has finalised a rudder-related rule stemming from the 2001 crash of an American Airlines Airbus A300 after take off from New York.
The agency on 21 November published a final rule requiring newly certificated aircraft with powered rudder-control surfaces to “be designed to withstand the loads caused by rapid reversals of the rudder pedals”.
“Pilots sometimes make rudder reversals during flight, even though such reversals are unnecessary and discouraged,” says the rule, which the FAA proposed in 2018. “The current design standards do not require the airplane structure to withstand the loads that may result from such reversals.”
The rule, which takes effect in about 60 days, will require manufacturers to demonstrate that new aircraft designs with powered rudder systems “can withstand an initial full rudder pedal input, followed by three full-pedal reversals at the maximum side-slip angle, followed by return of the rudder to neutral”.
Powered rudders include those that use electric (fly-by-wire) or hydraulic systems to move rudders based on rudder-pedal inputs made by pilots. Most modern large aircraft have fly-by-wire rudder systems.
The rule does not apply to aircraft with “mechanical” rudder controls, which typically involve cables linking pedals to the rudder itself. Boeing’s 737 Max has mechanical rudder controls, according to several reports.
The rule will apply to newly issued type certificates, though variants of existing aircraft types might also be subject to the change, according to the FAA.
The regulation’s impact on in-development aircraft remains unclear. But, the FAA anticipates only four in-development aircraft types, including two large aircraft and two business jets, will be affected during the next 10 years.
It does not specify those types but says all have fly-by-wire rudder systems.
The FAA also anticipates compliance will come at “minimal cost” to aircraft manufacturers – just $600,000 total for the two large aircraft and $470,000 total for the two business jets.
The rule stems from American flight 587, which crashed on 12 November 2001, killing all 260 people aboard and five people on the ground. After taking off from John F Kennedy International airport, bound for Santo Domingo, the aircraft experienced wake-induced turbulence from a Japan Air Lines Boeing 747-400.
In response, the first officer applied “cyclic rudder motions” – meaning left-then-right repeating rudder inputs. Those inputs caused the A300’s vertical stabiliser to fracture from “overstress”, causing the crash.
Flight 587 was the only “catastrophic” such rudder accident, but other similar non-fatal incidents are on record. Those include an A310 operated by German carrier Interflug in 1991, an American A300 over Florida in 1997, an Air Canada A319 in 2008 and a De Havilland Canada Dash 8-100 operated by Canadian carrier Provincial Airlines in 2005, says the FAA.