The Wall Street Journal
By ANDY PASZTOR
March 31, 2016 7:32 p.m. ET
U.S. Federal aviation regulators have issued a safety directive warning pilots flying Boeing Co.’s flagship 787 jetliners to avoid abrupt flight-control commands in the event of unreliable airspeed indications.
Following nonbinding recommendations that plane maker Boeing issued earlier in March to 787 operators world-wide, the Federal Aviation Administration on Thursday alerted cockpit crews that excessive pilot inputs under some circumstances amount to a safety hazard because they “could exceed the structural capability of the airplane.”
The agency ordered changes to the aircraft’s flight manual by the end of April, as an interim step while Boeing works on permanent modifications to the “crew alerting system, flight control system and air data system that will address the unsafe condition.”
The 787 fleet’s airspeed sensors, three separate devices called pitot tubes, are prone to some of the same problems that have plagued many other jetliner models over the years. “Significant water ingestion or simultaneous icing” of two of the tubes can cause the displayed speed to drop sharply below the plane’s actual speed, according to the FAA, and such “erroneous low airspeed” readings can lead to dangerous commands by pilots.
A Boeing spokeswoman said the company fully supports the directive and has worked “closely with the FAA to monitor the fleet and take appropriate actions.”
The FAA document was posted on the Federal Register website and mentioned three separate reports of in-service problems with airspeed sensors, without listing specific dates or carriers.
During one incident, according to the agency, a pilot failed to disconnect the autopilot before reacting to the erroneous low speed reading by abruptly pointing the plane’s nose downward. In this situation, when the aircraft is actually cruising at a high speed, the FAA determined such a response “could cause the airplane to exceed its structural capability.”
The revised manual, among other things, is supposed to stress “the need to disconnect the autopilot prior to making any manual fight control inputs.”
The FAA said it acted quickly to fix an unsafe condition, noting that the risk to the flying public “justifies waiving notice and (public) comment prior to adoption of this rule.” The directive directly applies to 43 planes operated by U.S. carriers, but foreign regulators eventually are expected to adopt it to cover hundreds of additional Boeing 787s.
The general problem of heavy rain or ice plugging pitot tube systems emerged as a major global safety issue after the fatal 2009 crash of an Air France Airbus A330 in the Atlantic. The crash investigation revealed that both the plane’s manufacturer and French regulators years earlier had recognized such hazards. But they failed to move aggressively to quickly replace suspect devices or step up pilot training focused on dealing with unreliable airspeed indications, especially at cruise altitude. Since then, regulators on both sides of the Atlantic have taken various steps to reduce such risks.
Nonetheless, questions about possible ice accumulation are still prominent in the minds of many experts as well as average fliers. Ice particles embedded in intense, high-altitude storms have caused pitot tubes to malfunction and contributed to other fatal jetliner crashes over the years. The best-known example, however, remains Air France Flight 447, which crashed nearly seven years go en route from Brazil to France, killing all 228 people on board.
Investigators determined that while flying through an area known for strong, high-altitude storms, the Air France crew failed to respond properly to unreliable airspeed indications, allowing the plane to slow too much and failing to get out of a deadly stall because they kept pulling the jet’s nose up at a sharp angle.
After Flight 447, European air-safety regulators issued safety directives mandating replacement and upgrades of pitot tube systems on Airbus jetliners, including A320s. In the fall of 2014, they issued a new mandate giving operators two years to make certain modifications because initial replacement parts didn’t demonstrate the necessary “level of robustness to withstand high-altitude ice crystals.”
The latest directive underscores that jet models designed years afterward also are susceptible to similar pitot tube system malfunctions caused by weather.
Original article can be found here: http://www.wsj.com