LAWTON, OK, USA
N396AE
Saab-Scania AB (Saab) 340B
During cruise flight, the flight crew reported smelling an odor similar to burning/smoldering electrical equipment and noticed that the landing gear control circuit breaker had popped. The flight crew consulted the company's Quick Reference Handbook (QRH). The QRH addressed hydraulic problems and failed to discuss possible electrical problems related to the operation of the landing gear. The company's maintenance facility was appraised of the situation; however, the maintenance person on duty was not able to assist the flight crew. Three tower fly-bys were made. The flight attendant and tower personnel reported that the landing gear appeared to be down and the gear doors were closed. The flight crew elected to land with the light on the gear handle indicating an 'in-transit' condition and the two main landing gear indicators in the 'unsafe' condition. The left main landing gear on the twin-engine transport category airplane collapsed during the landing roll. Examination revealed that the weight-on-wheels relay, which is located in the avionics bay directly under the captain's station, shorted, and as a result, the landing gear control circuit breaker popped. The electrical short was attributed to the spill of a soda can on the flight deck on a previous flight. The investigation revealed that the cockpit floor was not carpeted or sealed to prevent fluids/moisture from seeping into the electrical compartment beneath the cockpit floor. A review of the emergency extension system for the airplane revealed that the landing gear could have been extended if the fight crew had pulled the emergency extension handle.
On February 22, 1998, at 1021 central standard time, a Saab 340B transport category airplane, N396AE, operated by Simmons Airlines Inc., as American Eagle Flight 509, experienced a collapsed left main landing gear while landing at the Lawton-Fort Sill Regional Airport (LAW), near Lawton, Oklahoma. The passenger flight, which originated at the DFW International Airport at approximately 0919, was being operated under 14 Code of Federal Regulations Part 121. The airplane sustained minor damage and there were no injuries to the 3 passengers and 3 crewmembers aboard the airplane. Visual meteorological conditions prevailed and an IFR flight plan was filed for the scheduled 122-nautical mile flight. According to the operator, the flight crew reported that while en route to Lawton, in cruise flight at an assigned altitude of 12,000 feet, they smelled an odor similar to burning/smoldering electrical equipment and discovered that the landing gear control circuit breaker (F7) had popped. The flight crew notified their company's maintenance operations center (MOC) through dispatch, via radio, and after discussing all their options, elected to continue on to Lawton, which is one of the company's maintenance bases. As the flight approached Lawton, the flight crew pushed in the popped circuit breaker (F7), and the landing gear selector was placed in the extend (down) position. The flight crew stated that the landing gear began what seemed like a normal extension; however, the landing gear control circuit breaker (F7) popped again after approximately 5 seconds. The crew stated that the only indication displayed was the green (down and locked) light on the nose landing gear. Both main landing gear "down and locked" indicators were not illuminated, and the "in transit" light on the landing gear handle remained illuminated. The flight crew reported that they consulted the company's Quick Reference Handbook (QRH) and performed the "Landing Gear Will Not Extend" checklist. The note at the beginning of the procedure advises the flight crew to check the F7 circuit breaker and make sure it is in. Since this breaker had already been reset twice, the crew followed company procedures by not resetting the breaker for the third time. The QRH did not address or provide any guidance pertaining to a popped F7 circuit breaker. The flight crew requested that the flight attendant visually check the position of the landing gear from his vantage point in the cabin. The flight attendant reported that the landing gear appeared to be down and the main landing gear doors appeared to be closed. The flight crew elected to execute a tower fly-by for tower personnel to verify the position of the two main landing gears. Tower personnel reported that, "the gear appeared to be down" and the main "gear doors were closed." The pilot-in-command (PIC), who was serving as the non-flying pilot, appraised the company maintenance facility at LAW of their situation. The initial contact was made with one of their lead mechanics. Subsequently, when the flight crew reached the portion of the emergency checklist addressing the "gravity procedure," the PIC asked if the use of the emergency extension would be useful under the current situation. The maintenance person on the ground reported to the flight crew that the emergency handle would not offer a remedy to their present situation. The investigation revealed that the lead mechanic responding to the query from the flight crew had six months of experience with the operator. The investigation revealed that the QRH mainly addressed landing gear hydraulic problems and did not offer any guidance or cross reference to follow for electrical problems involving the landing gear, such as a popped F7 circuit breaker. A review of the emergency gear extension system for the airplane revealed that the landing gear could have been extended if the Emergency Extension Handle had been pulled by the flight crew. Prior to landing, the flight crew told the flight attendant that they were going to be making a "precautionary landing," and the passengers should be prepared for a "rough landing." The flight attendant, who was reported to have 7 weeks of experience as a flight attendant, did not prepare the cabin for an emergency landing. The flight attendant reported that he was not aware of the severity of the situation since he was not familiar with the terms "precautionary and rough landing." Following three tower fly-bys, the airplane was cleared to land on runway 35 with airport emergency equipment standing by. The flight crew reported that upon initial touchdown, they received a gear down (green light) indication on the right main landing gear, but never received one for the left main landing gear. Witnesses at the airport reported that the airplane touched down approximately 1,500 feet from the approach end of the 8,599 foot concrete runway. The left main landing gear collapsed as soon as weight was placed on the landing gear. The left propeller began to make contact with the runway approximately 300 feet after touchdown, and the airplane drifted to the left, exiting the runway approximately 2,300 feet from the point of touchdown. The airplane came to rest in a muddy area about 75 feet west of the edge of the runway, on a measured magnetic heading of 330 degrees. The control tower declared an emergency prior to the landing of the airplane. The airport's Crash and Fire Rescue (CFR) team was alerted. CFR equipment was pre-positioned on taxiway Charlie, on the right side of the runway. The airplane came to rest abeam taxiway Charley, on the left side of the runway. CFR personnel were at the airplane within 20 seconds after the airplane came to a stop on the grass. A member of the CFR team opened the left over-wing exit. All 3 passengers and 3 crewmembers exited the airplane safely through the left over-wing exit. No fire was reported. Airport authorities reported that three runway lights on the left side of the runway were "taken out by the airplane." The airport resumed normal operations at 1950 on the evening of the accident. The aircraft was reported to have 2,300 pounds of fuel remaining at the time of the incident. The operator estimated that there was sufficient fuel remaining for a 2-hour flight. The fuel system was not compromised and no fuel spilled during the landing sequence. Due to the resting attitude of the airplane, a small amount of fuel was reported to have leaked from an under-wing vent about an hour after the incident. Examination of the airplane by the FAA inspector confirmed minor damage to the left flap, left aileron, left horizontal stabilizer, landing gear doors and propeller. The inspector verbally released the airplane to the operator at 1455 for recovery to a secured hangar. Company maintenance personnel were able to recover the airplane to a hangar by 1955. Further post-recovery investigation revealed that a weight-on-wheels relay (P/N: M83536/6-022L), located at position 15 GA in an electrical control panel rack below the captain's floorboard, had shorted, which resulted in the landing gear control circuit breaker popping. A detailed visual examination of the relay revealed that the relay was coated with "a dark brown syrupy substance." The failure of the relay was attributed to the spill of soda on the flight deck on a previous flight. Examination of the cockpit revealed that the airplane was equipped with a cup holder for each of the flight crewmember stations. The size of the installed cup holders is not capable of holding a can of soda or a bottle of water. Cup holders used on other models of airplanes in the American Eagle fleet adjust to allow different size containers. The investigation also revealed that the cockpit floor is not carpeted or sealed to prevent fluids/moisture from seeping into the compartment beneath the cockpit. The airplane, serial number 340B-396, had accumulated a total of 3,578.9 hours on the airframe and engines at the time of the incident. The last inspection was performed on December 27, 1997, approximately 334 hours prior to the incident. A review of the maintenance records for the airframe and engines by an FAA inspector did not reveal evidence of any anomalies or uncorrected maintenance defects prior to the flight. Maintenance records indicated that the airplane was being maintained in accordance with the company FAA-approved continuous maintenance inspection program. The operator reported that the PIC was occupying the right seat and was acting as the non-flying pilot while administering initial operating experience (IOE) to the captain upgrade in the left seat. The second in command (SIC) recently upgraded to captain from a Saab 340 first officer, and was on his second day of IOE. Both flight crewmembers were on the second day of a 2-day sequence, consisting of 3 flight legs per day. They both had 3 days off prior to beginning the 2-day sequence on February 21, 1998. A review of the company's training syllabus for the flight crewmembers revealed that the "emergency landing gear extension" procedure is required during initial or upgrade training (in a simulator). The airplane was equipped with a Fairchild model A-100A cockpit voice recorder (CVR), serial number 62623. The recorder was removed from the airplane and transported to the NTSB audio laboratories on February 22, 1998. A CVR Group was formed and convened on March 9, 1998, to listen to the recorded media. A copy of the transcript is available in the public docket.
the collapse of the left main landing gear during landing roll as result of a shorted weight-on-wheels relay. Contributing factors were the insufficient information available to the flight crew in the company's quick reference handbook (QRH), and the manufacturer's inadequate protection of the weight-on-wheels relay from moisture.
Source: NTSB Aviation Accident Database
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