SEATTLE, WA, USA
N921R
McDonnell Douglas DC-8-63F
The flight was cleared for an instrument landing system (ILS) approach. The ceiling was 200 feet overcast, visibility was 1 mile (runway visual range was greater than 6,000 feet) and the first officer was the pilot flying (according to company operating procedures, the minimum ceiling for first officer flying is normally 500 feet.) Air traffic control (ATC) radar indicated that the aircraft was left of the localizer course and/or below glide path, outside of the company's stabilized approach limits, for the majority of the final approach segment below 1,000 feet above touchdown. The aircraft broke out approximately at minimums (200 feet above touchdown), left of (and diverging away from) the runway centerline. The captain called, "push it down, push it down, push it down", and asked, "you got it or you want me to get it?". The first officer replied, "I can get it", and the captain said, "OK." The aircraft pitched down and banked up to approximately 14 degrees in correcting back to the runway. A high sink rate existed in the last few seconds before touchdown; the flight data recorder registered a vertical acceleration of about 1.8 G at touchdown. The aircraft's number 1 main landing gear wheel separated from the aircraft at or shortly after touchdown. The separated wheel entered the airport ramp area and struck two parked trucks and a baggage cart in front of the main passenger terminal. Post-incident examinations of the aircraft's number 1 wheel retaining nut disclosed that the nut threads were worn approximately 0.030 inch beyond engineering drawing specifications. FAA guidance directs FAA principal operations inspectors (POIs) to ensure their operators' operations manuals contain stabilized approach criteria as well as required actions in the event of deviations ("i.e. missed approach or go/around [sic]"). The company's DC-8 operations manual states only that deviations from the stabilized approach profile "are cause for consideration to abandon the approach."
HISTORY OF FLIGHT On July 18, 1998, approximately 0700 Pacific daylight time, Emery Worldwide Airlines flight 26, a Boeing (formerly McDonnell Douglas) DC-8-63F, N921R, experienced a separation of the number 1 main landing gear wheel from the aircraft upon landing at Seattle-Tacoma International Airport, Seattle, Washington. Following the separation, the wheel entered the Horizon Air ramp area (in front of the airport main terminal building's C concourse) and struck a Horizon Air maintenance truck parked adjacent to gate C4, damaged one other vehicle and a baggage cart, and sent debris through a window of the Horizon Air maintenance office in the main terminal building. The airplane sustained minor damage in the incident and there were no injuries to the airline transport pilot-in-command, first officer, flight engineer, or two jumpseating crewmembers aboard the aircraft, nor were there any injuries to persons on the ground. Instrument meteorological conditions (IMC) existed at the time of the incident, and an instrument flight rules (IFR) flight plan had been filed for the 14 CFR 121 non-scheduled domestic cargo flight from Dayton, Ohio. The flight was cleared by air traffic control (ATC) for the instrument landing system/distance measuring equipment (ILS/DME) approach to runway 34R. Crew statements and log entries indicated that the first officer, whom a representative of Emery reported had been with the company for approximately 9 months, was the pilot flying at the time of the incident. The first officer reported that during the approach, "I decided to try using the command bars during the descent and turned them off after intercepting final when they started giving me erroneous turns." The flight crew's statements indicated that the aircraft broke out of the weather at minimums, left of centerline. The first officer reported that at this point, the captain asked him if he thought he could continue and he replied affirmatively and aligned himself with the runway. The first officer stated that as he passed the threshold, the aircraft was on centerline and airspeed, and that as he began the landing flare the right wing dipped slightly. The first officer stated that the captain assisted on the controls to neutralize the wings. He reported that the landing was in the touchdown zone with the right main gear touching first, and that the spoilers did not automatically deploy upon landing (the flight engineer also indicated that they did not automatically deploy, that they were armed, and that he deployed them manually; however, the flight crew did not indicate any discrepancies with the spoiler system in the aircraft log after the flight.) The statements of the flight crew and jumpseating crewmembers indicated that they did not observe anything that would cause the wheel to depart the aircraft (one jumpseater reported that "The first and only indication we had of a problem was the tower report that a tire had departed from the aircraft.") Five witnesses (two Seattle tower controllers including the one on duty at the Local Control position, two Port of Seattle ramp controllers, and a Horizon Air ground service agent) provided statements to investigators. Of the five witnesses, three reported they observed the aircraft's wings rocking on approach, with one witness reporting that the airplane went right of the runway centerline just before touchdown and that the aircraft's left wing almost contacted the ground. One witness also reported that the airplane was "making over correct[ion]" or "trying to correct" when landing. Additionally, two witnesses reported either that the aircraft's right wing dipped just before touchdown, or that the airplane made a right bank just before touchdown. One witness reported that the airplane dropped just before touchdown, with three witnesses reporting that the airplane landed either "hard" or "rough" (the witness who described the landing as "rough" stated that the airplane did "not [make] an excessive flare.") Two witnesses reported that the airplane landed on one side first (one of these stated it landed on the right side first.) Two witnesses reported the airplane bounced after touchdown (one of these reported it bounced about 20 feet back into the air), with one witness reporting seeing two puffs of smoke from the aircraft's tires. One witness reported that the wheel separated at touchdown, one reported she observed it separated in the touchdown area, one reported that it separated during the touchdown-bounce-settle back to the runway sequence, and one witness reported he observed the wheel separate after touchdown. Two witnesses reported that the aircraft's touchdown point was between taxiways R and Q (taxiway R intersects the runway approximately 2,000 feet past the threshold, and taxiway Q intersects the runway approximately 2,500 feet past the threshold) and one witness reported that the aircraft touched down north of taxiway P, which intersects the runway approximately 2,900 feet past the threshold. ATC radar data on the aircraft, furnished by Seattle approach control, was sent to the NTSB's Vehicle Performance Division in Washington, D.C., which produced a study of the radar data (attached). The radar study depicted the aircraft's recorded radar positions over time in relation to the airport runways and the runway 34R localizer and glide slope. According to the radar study, the plots showed the aircraft initially lining up slightly left of the runway 34R localizer centerline, returning to the localizer centerline, then (at 0657:53) deviating generally away from, and remaining left of, the localizer centerline for 1 minute and 38 seconds, until 0659:31. The aircraft reached a maximum deviation of approximately 3/8 of full-scale displacement (about 3/4 dot deviation) at 0659:07, before beginning to track back toward the localizer centerline. The aircraft altitude at 0659:07 was recorded as 1,200 feet. The aircraft was back within approximately 1/4 scale (1/2 dot) deviation at 0659:26 (altitude 1,000 feet), and was back on the localizer centerline at 0659:31 (altitude 900 feet). It remained approximately on centerline from 0659:31 to 0659:44, then deviated slightly less than 1/4 scale (1/2 dot) right of centerline from 0659:49 to 0659:54, and subsequently crossed back through the localizer centerline from right to left and diverged away from centerline to the left. The aircraft reached a maximum deviation of between 3/4-scale (1 1/2 dots) and full-scale (2 dots) to the left of centerline at 0700:12 and 500 feet before turning and tracking back toward the landing runway. The radar study showed the aircraft as being nearly on glide path at an altitude of approximately 2,000 feet and 5.5 nautical miles from the threshold of runway 34R. From 1,500 feet down to 800 feet, the aircraft was shown as going below glide path; it reached approximately 1/2 scale (1 dot) low at 1,200 feet and remained generally 1/2 scale or more below glide path from 1,200 feet down to 800 feet, where it was shown as being close to a full-scale low deviation. The aircraft was shown as leveling at 800 feet until recapturing the glide path from below. Below 800 feet, the aircraft was shown as fluctuating about the glide path but remaining mainly below it. The aircraft's altitude immediately prior to crossing the runway 34R threshold (0700:17) was reported as 400 feet, and immediately after crossing the threshold (0700:21) was given as 300 feet. Subsequent plots of the aircraft in the vicinity of the runway showed the aircraft's altitude as 200 feet, increasing to 300 feet. (NOTE: The actual touchdown zone elevation is 368 feet. In the radar data, aircraft altitudes were recorded to the nearest 100 feet.) FAA Flight Standards Handbook Bulletin for Air Transportation (HBAT) 98-22, "Stabilized Approaches", dated May 26, 1998, directs FAA principal operations inspectors (POIs) with certificate management responsibilities for 14 CFR 121 air carrier operating certificate holders to review their operators' training and operations manuals to ensure that the concept of stabilized approach configurations is addressed. HBAT 98-22 further directs POIs to "ensure that their operator's operations and training manuals contain criteria for the stabilized approach as referenced in FAA Order 8400.10, Air Transportation Operations Inspector's Handbook...." HBAT 98-22 directs that the operator's operations and training manuals shall contain, among other items, "Minimum requirements for the stabilized approach and the immediate actions needed to be taken if the stabilized approach conditions are not met (i.e., missed approach or go/around [sic])...." Emery's DC-8 Aircraft Operating Manual, revision number 29 (effective June 22, 1998) defines a stabilized approach, with respect to localizer and glide slope, as being within 1/2 dot (1/4 scale needle deflection) on the localizer and 1/2 dot (1/4 scale needle deflection) on the glide slope. The manual indicates that it is mandatory to be stabilized by 1,000 feet height above the airport when in IMC, and states: "Any deviation from the stabilized approach profile will be cause for consideration to abandon the approach." The incident aircraft was equipped with a cockpit voice recorder (CVR) and flight data recorder (FDR). The CVR and FDR were removed from the aircraft following the incident and sent to the NTSB Vehicle Recorders Division in Washington, D.C., for readout. Pertinent data from the CVR and FDR readouts is presented in the FLIGHT RECORDERS section below. OTHER DAMAGE The impact of the separated main gear wheel from Emery 26 (the weight of the wheel and tire assembly is approximately 307 pounds, according to the aircraft maintenance manual) damaged a parked Horizon Air maintenance truck, a baggage tug and a baggage cart, and also sent small debris through the window of the Horizon Air maintenance office located at ramp level in the Seattle-Tacoma International Airport main terminal building. The maintenance truck the wheel struck was parked in front of the Horizon Air maintenance office, and blocked the wheel from entering the Horizon Air maintenance office. Damage to the Horizon van was reported by the Port of Seattle Police as being in excess of $6,000.00. The wheel also knocked over a ladder in the ramp area, which struck a van registered to the ESTEY Corporation resulting in cosmetic damage to the ESTEY van. There was no damage to the tug and minor damage to the baggage cart. AIRCRAFT INFORMATION The incident aircraft, a McDonnell Douglas DC-8-63F (fuselage number 548, serial number 46145), was initially delivered by McDonnell Douglas on May 26, 1971. The aircraft had 64,037.7 total airframe hours and 20,866 landings at the time of the incident, according to a copy of the aircraft maintenance log. Emery reported that the airplane had last received a continuous airworthiness inspection on July 11, 1998, one week and 60 flight hours before the incident. According to copies of the aircraft maintenance records furnished to the FAA by Emery, the aircraft's number 1 main landing gear wheel and tire were changed on June 29, 1998, at 63,933.0 airframe hours and 20,820 landings. The Emery mechanic who stated he performed the wheel and tire change prepared a statement indicating that the change was performed per McDonnell Douglas DC-8 Maintenance Manual 32-40-1, and that no defects were noted to the wheel and tire assembly at that time. Emery reported that a computer record search conducted by the airline for "any & all ILS & DME work done on [the] aircraft" from March 1, 1998, to January 2000, disclosed no corresponding aircraft maintenance record entries. The aircraft's weight and balance/load manifest, prepared by the first officer, indicated a planned landing weight of 245,388 pounds. The aircraft's maximum landing weight is 275,000 pounds, according to the aircraft load planning documentation. According to an excerpt from the DC-8 Operation Manual furnished by Boeing's Douglas Products Division, the airplane landing limit load factor is determined by two conditions: "first, landing at the maximum certified landing weight...for a 600 foot-per-minute [10 feet per second] rate of descent; and second, landing at the maximum certified takeoff gross weight...for a 360 foot-per-minute [6 feet per second] rate of descent." METEOROLOGICAL INFORMATION According to the National Oceanic and Atmospheric Administration (NOAA) Internet METAR observation archive, the ceiling at Seattle-Tacoma on the day of the incident was 200 feet overcast from 0439 until 0823. The ceiling improved to 200 feet broken (with 500 feet overcast) at 0856, to 300 feet broken (with 600 feet overcast) at 0936, and to 800 feet broken at 0944. Weather conditions reported in the Seattle-Tacoma 0557 hourly observation were: ceiling 200 feet overcast; visibility 1 1/4 statute miles in fog; runway 16R runway visual range (RVR) variable from 3,000 to 6,000 feet; temperature and dewpoint 13 degrees C; wind from 220 degrees at 5 knots; and altimeter 30.06 inches Hg. Conditions were reported in the next observation (at 0656) as: ceiling 200 feet overcast; visibility 1 statute mile in fog; runway 34R runway visual range (RVR) greater than 6,000 feet; temperature 14 degrees C; dewpoint 13 degrees C; winds variable at 4 knots; and altimeter 30.07 inches Hg. In his statement, the first officer stated: "We knew leaving Dayton that the weather in Seattle was at minimums and updated the weather many times enroute." FAA air traffic control transcripts indicated that upon check-in on frequency with Seattle Approach at 0648:11, the crew of Emery 26 indicated they had Seattle-Tacoma automatic terminal information service (ATIS) information "Juliet". Seattle Approach replied that information "Kilo" was then current, and that the runway 34R RVR was more than 6,000 feet. The crew of Emery 26 replied that they would get information "Kilo". Seattle Tower again informed the crew that the runway 34R RVR was "more than six thousand" at 0657:27, upon clearing Emery 26 to land. Emery's General Operations Manual dated January 6, 1997, states that the captain will not allow the first officer to fly an approach below weather minimums of 500 foot ceiling and 1 mile visibility "except in unusual circumstances." AIDS TO NAVIGATION At the time of the incident, the published ILS DME runway 34R (I-SEA) final approach course was 338 degrees magnetic. The published final approach course was based on a 1965 magnetic variation value of 22 degrees East (at the time of the incident, the actual magnetic variation at the airport was 19.05 degrees East.) According to FAA airways facilities officials, the I-SEA localizer centerline is aligned with the runway 34R centerline. The I-SEA glide slope angle is 2.75 degrees. The published minimum runway visual range (RVR) for a full system ILS approach to this runway is 1,800 feet. Decision height (DH) for the approach is 568 feet above sea level (MSL) (200 feet above the touchdown zone elevation of 368 feet MSL), and threshold crossing height is 64 feet. The FAA furnished records of flight inspections conducted on the runway 34R localizer on August 8, 1997, March 16, 1998, and February 9, 1999. The flight inspection reports documented that during the February 9, 1999, flight inspection, the localizer course width was found to be out of tolerance when intentionally adjusted to a "wide alarm" condition (the system did not automatically shut off until reaching a course width of 3.83 degrees, with a maximum allowable course width of 3.79 degrees at system shutoff.) However, examination of flight and ground inspection results from the February 1997 to March 2000 time period disclosed that the normal, "as-found" localizer course width and alignment were within acceptable tolerances, and were stable to within approximately 2% for width and 3 microamperes for alignment, during that entire time frame. AERODROME AND GROUND FACILITIES Seattle-Tacoma International runway 34R is 11,900 feet long and 150 feet wide, and is oriented on a heading of 000.34 degrees true (341.29 degrees magnetic at the time of the incident, based on actual ma
The flight crew's failure to perform a missed approach upon failing to attain and/or maintain proper course/runway alignment and glidepath on final approach, resulting in a high-sink-rate landing and subsequent separation of a main landing gear wheel from the aircraft. Factors contributing to the incident included: low ceiling; the first officer's failure to attain and/or maintain proper course/runway alignment and glidepath on approach; insufficiently defined company procedures for responding to deviations from a stabilized approach profile; inadequate FAA principal operations inspector approval of company operating procedures; and a worn main landing gear wheel retaining nut.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
