Pratt & Whitney
Canada, and the operators of EMB-120
airplanes, coordinated an inspection of the worldwide fleet and discovered many other airplanes with missing drain plugs that were subsequently capped, eliminating a fire hazard. Safety Board investigations have resulted in findings of inadequate design or certification of particular aircraft components. For example, on April 5, 1991
, an Atlantic Southeast Airlines EMB-120 crashed near Brunswick
, killing all 23 persons aboard.
The Safety Board found that severe wear of a component in the propeller control unit on the airplane’s left engine resulted in asymmetrical lift and thrust, rendering the aircraft uncontrollable. During its investigation, the Board learned of three previous occasions when operators found that a propeller would not operate properly during ground tests. Based on Board recommendations, the FAA required additional inspections of propeller control units and the installation of a fail-safe feature to prevent the propeller blade angle from rotating below the flight idle position while in flight.
In August 1995, an Atlantic Southeast Airlines EMB-120 turbo propeller engine-powered airplane crashed near Carrollton, Georgia, following a propeller blade separation and secondary in-flight damage to the airplane. The Safety Board’s investigation determined that the imbalance caused by the failed propeller blade displaced the engine from its mounts, resulting in drag. The drag resulted in a loss of control in an attempted forced landing. The Safety Board's investigation revealed that the failed propeller blade had been recently removed and returned to service following an inspection that had detected indications of the crack. However, that inspection by the manufacturer' repair station did not detect the crack that led to the in-flight failure. It had been masked by an improper repair procedure which eliminated the crack indication. The Safety Board subsequently recommended the removal from service within five days of all blades that had similar inspection indications and repairs. The Safety Board’s investigation also brought about improvements in ultrasonic inspection techniques, blade repair procedures, technician training, and corporate policies on flight safety critical components.
Changes recommended by the Board as a result of one tragedy can prevent another. Almost 25 years ago, on March 3, 1974, a Turkish Airlines DC-10 crashed near Paris, France, when the lower aft cargo door separated in flight during climbout. The resultant explosive decompression caused the cabin floor to buckle downward and jam the flight control cables. All 346 persons aboard perished. Safety Board recommendations that stemmed from that investigation led to the installation of blowout pressure relief panels in the cabin floors of all widebody airplanes.
On February 24, 1989, a United Airlines Boeing 747 en route from Honolulu, Hawaii, to New Zealand with 355 persons aboard lost the forward lower lobe cargo door during climbout. Although nine occupants were killed in the accident, the catastrophic loss of the entire airplane and its occupants was prevented by the opening of the pressure relief doors in the cabin floor. While the cabin floor was damaged, the control cables remained functional because of the modifications required after the Turkish Airlines accident.
Another widebody airliner had a different problem that has since been corrected following Safety Board recommendations. On April 6, 1993, during a flight from Shanghai, China, to Los Angeles, a China Eastern Airlines MD-11 experienced an inadvertent deployment of all leading-edge wing slats while at 33,000 feet over the Pacific Ocean. The resulting severe pitch oscillations led to two fatalities and 160 injuries. Based on results of the Safety Board investigation, McDonnell Douglas worked with the FAA and aircraft operators to redesign the MD-11 flap/slat handle, and reduce the potential for inadvertent slat operation. In addition, the Board identified that flight crews needed additional training related to the high-altitude handling qualities of the MD-11 and DC-10 aircraft.
On May 5, 1991, a Lauda Air Boeing 767-300ER experienced an uncommanded in-flight deployment of the number one engine thrust reverser, while climbing through 24,700 feet, approximately 16 minutes after takeoff from Bangkok, Thailand. The pilots lost control, the airplane entered a steep dive, exceeded the maximum velocity and crashed, killing all 223 people aboard. The investigation by the Thai air worthiness authorities and the Safety Board revealed the possibility of an in-flight thrust reverser deployment, shortcomings in the fail-safe thrust reverser design requirement on 767 airplanes, and lack of flightcrew operational procedures to address such an anomaly. Design changes to engine reverser systems that have been introduced and mandated as a result of this accident have greatly reduced the possibility of an in-flight thrust reverser deployment in the 767 and many other air carrier aircraft models.
There are many other examples of specific aircraft design problems discovered by the Safety Board. Here are some of them:
- On December 29, 1991, a China Airlines Boeing 747 freighter crashed about five minutes after takeoff near Taipei, Taiwan, and on April 10, 1992, an El Al Boeing 747-200 freighter crashed into two nine-story apartment buildings while returning to land after takeoff from Amsterdam, Netherlands. The investigations of both accidents revealed that during climb, the No. 3 engine and pylon had separated from the wing, collided with the No. 4 engine and caused the separation of that engine. The combined effects of asymmetrical weight, thrust, and drag caused the pilots to lose control. The investigations revealed that the failed fuse pins in the pylon-to-wing attachment fittings had cracks stemming from corrosion pits. As a result of the Safety Board's involvement in the Taiwanese and Dutch investigations, inspection procedures were modified and an improved fuse pin was designed and installed in all Boeing 747s reducing the likelihood of a repeat of such accidents.
- Following the Board's investigation of a 1990 runway collision in Detroit that killed a flight attendant and seven passengers, redesigned emergency tailcone release handles are now required on all commercial and militar y DC-9s and MD-80s to assure the availability of this exit in the event of an emergency.
- During the Safety Board's exhaustive investigation of the crash of a USAir Boeing 737 near Pittsburgh on September 8, 1994, that claimed 132 lives, investigators found that rudder anomalies could be produced in laboratory tests. In October 1996, the Board recommended numererous rudder design changes to older 737s. The FAA and Boeing agreed in 1996 to retrofit older 737s with a new rudder system design.
- In May 1997, a Skywest Airlines EMB-120 had an in-flight fire in the No. 2 engine after takeoff from San Diego, California. The Safety Board’s investigation determined that a missing drain plug in the Pratt & Whitney Canada PW100 engine may have allowed fuel to drain into the hot engine compartment and caused the fire. During the investigation, the Safety Board, Embraer, Pratt & Whitney Canada, and the operators of EMB-120 airplanes coordinated an inspection of the worldwide fleet and discovered many other airplanes with missing drain plugs that were subsequently capped, eliminating a fire hazard.
- In general aviation, a Safety Board recommendation led to an FAA airworthiness directive in 1993 to repair corrosion and cracking in the wing front spar fuselage attachment assembly on Piper PA-25 airplanes. Left uncorrected, the problem could have led to in-flight wing separations. More than 1,200 aircraft were affected by the directive.