# NTSB DEN93FA049: Mcdonnell Douglas DC-9-82, N72822, Denver, CO, April 27, 1993 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Field investigation · Final report - Date: April 27, 1993, 17:28 local (23:28 UTC) - Place: Denver, CO - Coordinates: 39.760902, -104.920059 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.7609&lon=-104.9201&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 2 minor, 119 uninjured - Status: Completed, report June 30, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 11076 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN93FA049 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/11076/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=11076 - Page: https://openairdocs.org/ntsb/DEN93FA049 ## Probable cause A VIBRATION IN THE RIGHT MAIN LANDING GEAR, FOR UNDETERMINED REASONS, WHICH RESULTED IN COLLAPSE OF THE RIGHT MAIN GEAR. A FACTOR WAS FAILURE OF THE PILOT IN COMMAND TO ENSURE DEPLOYMENT OF THE GROUND SPOILERS. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Main gear collapsed, landing - roll - spoiler extension - not performed, pilot in command (contributing factor) - landing gear,main gear - vibration (cause) - reason for occurrence undetermined (cause) - landing gear,main gear - failure,total - landing gear,main gear - overload ## Analysis FOLLOWING TOUCHDOWN A LANDING GEAR VIBRATION OCCURRED WHICH LED TO A COLLAPSE OF THE RIGHT MAIN LANDING GEAR AT 117 KNOTS. THE RIGHT WING CONTACTED THE RUNWAY AND THE AIRPLANE SKIDDED TO A STOP ON THE RUNWAY AS IT ENTERED THE OVERRUN. DURING THE ENSUING EMERGENCY EVACUATION TWO PASSENGERS SUSTAINED MINOR INJURIES. EXAMINATION OF APPLICABLE COMPONENTS DID NOT PROVIDE A SPECIFIC CAUSE FOR THE VIBRATION THAT LED TO THE COLLAPSE. THREADS ON THE RIGHT GEAR APEX BOLT FAILED RESULTING IN THE GEAR'S 90 DEGREE ROTATION AND THE SUBSEQUENT OVERLOAD COLLAPSE. THE GROUND SPOILERS DID NOT ACTIVATE AND THE CREW STATED THAT THEY HAD ARMED AUTO SPOILERS. THE MANUFACTURER REPORTED THAT THERE HAVE BEEN A TOTAL OF THREE SIMILAR NON-FLIGHT TEST OCCURRENCES. IN ALL THREE EVENTS THE GROUND SPOILERS DID NOT EXTEND. ## Factual narrative HISTORY OF FLIGHT on April 27, 1993, at 1728 mountain daylight time, a McDonnell Douglas DC-9-82, N72822, operating as Continental Airlines Flight 588, had the right main landing gear collapse during landing roll at Stapleton International Airport, Denver, Colorado. There were two minor injuries reported from the emergency evacuation, and the aircraft sustained substantial damage. The aircraft was being operated under 14 CFR Part 121 when the accident occurred. Visual meteorological conditions prevailed and an IFR flight plan was filed for this scheduled flight from San Francisco, California, which originated at 1515 mountain daylight time. According to the flight deck crew, the takeoff, en route, and approach were normal. Upon touch down on runway 26R, a severe vibration occurred and the right main gear collapsed at what the copilot recalled to be 60 knots. The aircraft remained on the runway and skidded to a stop. PERSONNEL INFORMATION Flight experience and flight deck crew qualifications are depicted in this document. The pilots' had a reported, combined, flight experience in this type of aircraft of 11,600 hours. Both were properly qualified and current to conduct the flight. FLIGHT RECORDERS The flight data and voice recorder were analyzed at the National Transportation Safety Board Laboratory. The voice recorder contained no information pertinent to the accident. The flight recorder information is attached and provides information that the approach was within normal parameters and that touchdown occurred at 134 knots indicated airspeed. According to the recorded data, the right main gear collapsed at approximately 117 knots at which time the heading changed approximately 5 degrees to the left. There is no indication via the recorded information that the ground spoilers deployed following landing. WRECKAGE AND IMPACT INFORMATION Runway witness marks provided no information that an abnormal touchdown occurred, and the actual point of touchdown could not be determined. Witness marks on the runway are computed from the approach end and indicate that at 3,500 feet, the left main landing gear tires left marks associated with a shimmy. At 3,600 feet, the right inboard tire left heavy marks, and at 3,750 feet, metal deposits from the right wing structure began. Also at 3,750 feet, the right main tire marks indicate that the right wheel assembly turned 90 degrees to the direction of travel and remained fixed in that position throughout the remainder of the aircraft travel. The aircraft came to a stop 8,600 feet from the approach end of the runway at the beginning of the overrun approximately 30 feet right of centerline. A detailed wreckage diagram and photographs are attached. TESTS AND RESEARCH Applicable components from the right main landing gear assembly, brakes, anti-skid, and spoilers were shipped to the facilities of McDonnell Douglas and/or Continental Airlines for further examination. The results of the examinations are attached and provide no definitive data as to the initiation of the vibration which lead to the gear collapse. The tests did reveal that the threads on the right gear apex bolt failed causing the nut to depart and allowed the right main gear to rotate 90 degrees, bending the lower torque link and damaging the flange bushings and spacers on the left torque link. Ultimately, the gear collapsed as a result of overload on the side brace of the right main landing gear. Research and tests are continuing; however, as a result of the work done to date, McDonnell Douglas issued an ALL OPERATORS LETTER (AOL), with recommended alterations to operating procedures. A copy of that AOL is attached. It also addresses the fact that there have been three other similar in- service events. In all three cases the spoiler non extension was a common denominator. As a result of the flight data recorder information, it was determined that the aircraft ground spoilers did not activate and the crew stated that they armed the spoilers. Tests on those components revealed no discrepancies which would have prevented deployment. ADDITIONAL INFORMATION The aircraft was verbally released to Continental Airlines on April 28, 1993, following examination and identification of components to be retained. The retained components are being returned to Continental upon completion of additional testing. ## Aircraft - Registration: [N72822](https://openairdocs.org/deregistered/N72822-2005-09-26), registration cancelled 2005-09-26, S/N 49482, built 1986 (OpenAirDocs) - Reported make and model: MCDONNELL DOUGLAS DC-9-82 - Registry model: [Mcdonnell Douglas DC-9-82(MD-82)](https://openairdocs.org/model/mcdonnell-douglas-dc-9-82-md-82) (registry code 3022082) (OpenAirDocs) - Registry engine: [Pratt & Whitney JT8D series](https://openairdocs.org/engine/pratt-whitney-jt8d-series) (registry code 52053, turbo-jet) (OpenAirDocs) - Category: Airplane - Serial number: 49482 - Airframe hours: 21572 - Engines: P&W JT8D-217 20750 lbs thrust turbo jet - Damage: Substantial damage - Flight: Part 121 - Registered owner: Continental Airlines - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, April 1, 1993, 252 hours before - Departed: SFO, SAN FRANCISCO, CA - Flight plan: IFR - Airport: DEN, Stapleton International, runway 26R, 8,599 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 49; airline transport; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 25,000 total, 5,600 in this make and model, 7,000 as pilot in command, 210 in the last 90 days, 70 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 16 knots - Visibility: 50 statute miles - Lowest ceiling: 6,500 ft broken - Temperature: 63 °F, dew point 36 °F - Altimeter: 30.00 inHg - Observed at: DEN, 1 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19930427017299A](https://openairdocs.org/incident/19930427017299A), Apr 27, 1993: Doug DC982, Denver, CO, Substantial damage. Severe vibration landing. Right main gear collapsed. Apex bolt failed. Castered gear. Non extension ground spoilers ## Other investigations on N72822 (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB DEN93IA005](https://openairdocs.org/ntsb/DEN93IA005), Oct 13, 1992: Mcdonnell Douglas DC-9-82 (N72822), Denver, CO, incident, minor damage. Probable cause: AN INADVERTENT ATTEMPT, BY UNKNOWN PERSONS, TO START THE APU WHICH HAD BEEN PLACARDED AS INOPERATIVE. FACTORS WERE: INADEQUATE PROCEDURES IN RENDERING THE APU INCAPABLE OF BEING STARTED WHEN… ## Docket (34 files) The files NTSB released with the investigation on January 18, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=11076. 4.8 MB in all. - Supplement c (item 1, PDF, 4 pages, 328 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956422&FileExtension=pdf&FileName=Supplement%20C-Master-Rel.pdf - Supplement d (item 2, PDF, 6 pages, 343 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956193&FileExtension=pdf&FileName=Supplement%20D-Master-Rel.pdf - Supplement e (item 3, PDF, 2 pages, 133 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956555&FileExtension=pdf&FileName=Supplement%20E-Master-Rel.pdf - Supplement s (item 4, PDF, 1 page, 37 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956313&FileExtension=pdf&FileName=Supplement%20S-Master-Rel.pdf - Pilot-operator aircraft accident report NTSB form 61201-2 (item 5, PDF, 6 pages, 590 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956121&FileExtension=pdf&FileName=Pilot-Operator%20Aircraft%20Accident%20Report%20NTSB%20Form%2061201-2-Master-Rel.pdf - Flight data recorder information (item 6, PDF, 34 pages, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956966&FileExtension=pdf&FileName=Flight%20Data%20Recorder%20Information-Master-Rel.pdf - Wreckage diagram (item 7, PDF, 2 pages, 85 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956698&FileExtension=pdf&FileName=Wreckage%20Diagram-Master-Rel.pdf - Applicable portions of ATC package (item 8, PDF, 11 pages, 297 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956124&FileExtension=pdf&FileName=Applicable%20Portions%20of%20ATC%20Package-Master-Rel.pdf - Release of aircraft wreckage NTSB form 612015 (item 9, PDF, 1 page, 67 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956576&FileExtension=pdf&FileName=Release%20of%20Aircraft%20Wreckage%20NTSB%20Form%20612015-Master-Rel.pdf - Photo 4 looking forward along right side of aircraft note; right main gear is 90 degrees to the aircraft direction (item 10, PDF, 1 page, 29 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956800&FileExtension=pdf&FileName=Photo%204%20%20Looking%20forward%20along%20right%20side%20of%20aircraft%20%20Note;%20%20right%20main%20gear%20is%2090%20degrees%20to%20the%20aircraft%20direc-Master-Rel.pdf - Photo 5 right wing (item 11, PDF, 1 page, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467313&FileExtension=pdf&FileName=Photo%205%20%20Right%20wing-Master.pdf - Photo 6 right main gear as viewed from outboard of gear well under right wing (item 12, PDF, 1 page, 36 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467315&FileExtension=pdf&FileName=Photo%206%20%20Right%20main%20gear%20as%20viewed%20from%20outboard%20of%20gear%20well%20under%20right%20wing-Master.pdf - Photo 7 left main landing gear (item 13, PDF, 1 page, 38 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467317&FileExtension=pdf&FileName=Photo%207%20%20Left%20main%20landing%20gear-Master.pdf - Photo 8 skid marks looking toward approach end of runway at gear swivel point (item 14, PDF, 1 page, 35 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467319&FileExtension=pdf&FileName=Photo%208%20%20Skid%20marks%20looking%20toward%20approach%20end%20of%20runway%20at%20gear%20swivel%20point-Master.pdf - Photo 9 skid marks looking toward approach end of runway from directly behind aircraft (item 15, PDF, 1 page, 27 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467321&FileExtension=pdf&FileName=Photo%209%20%20Skid%20marks%20looking%20toward%20approach%20end%20of%20runway%20from%20directly%20behind%20aircraft-Master.pdf - Photo 10 right main gear looking forward down right side of aircraft (item 16, PDF, 1 page, 37 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467323&FileExtension=pdf&FileName=Photo%2010%20%20Right%20main%20gear%20looking%20forward%20down%20right%20side%20of%20aircraft-Master.pdf - Photo 501 93-N-686 RH shimmy damper assembly as-received with the apex bolt arrow still in place mag 4X (item 17, PDF, 1 page, 24 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467325&FileExtension=pdf&FileName=Photo%20501%20%2093-N-686%20RH%20shimmy%20damper%20assembly%20as-received%20with%20the%20Apex%20Bolt%20arrow%20still%20in%20place%20%20Mag%204X-Master.pdf - Photo 502 93-N-691 exploded view of the RH shimmy damper assembly-apex bolt has been removed mag 2X (item 18, PDF, 1 page, 22 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467327&FileExtension=pdf&FileName=Photo%20502%20%2093-N-691%20Exploded%20view%20of%20the%20RH%20shimmy%20damper%20assembly-Apex%20bolt%20has%20been%20removed%20%20Mag%202X-Master.pdf - Photo 503 93-N-799 over-all view of the shimmy damper reservoir note the severe damage and thread separation ident (item 19, PDF, 1 page, 26 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467329&FileExtension=pdf&FileName=Photo%20503%20%2093-N-799%20Over-all%20view%20of%20the%20shimmy%20damper%20reservoir%20%20Note%20the%20severe%20damage%20and%20thread%20separation%20%20I-Master.pdf - Photo 504 93-N-718 LH shimmy damper as-received this assembly sustained no damage mag 5X (item 20, PDF, 1 page, 32 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467331&FileExtension=pdf&FileName=Photo%20504%20%2093-N-718%20LH%20shimmy%20damper%20as-received%20%20This%20assembly%20sustained%20no%20damage%20%20Mag%205X-Master.pdf - Photo 505 93-N-706 over-all view of the failed bungee cylinder note the separated piston end arrow (item 21, PDF, 1 page, 28 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467333&FileExtension=pdf&FileName=Photo%20505%20%2093-N-706%20%20Over-all%20view%20of%20the%20failed%20bungee%20cylinder%20%20Note%20the%20separated%20piston%20end%20arrow-Master.pdf - Photo 506 93-N-705 close-up of the bungee cylinder piston as-received note severe damage to entire fracture face (item 22, PDF, 1 page, 32 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467335&FileExtension=pdf&FileName=Photo%20506%20%2093-N-705%20%20Close-up%20of%20the%20bungee%20cylinder%20piston%20as-received%20%20Note%20severe%20damage%20to%20entire%20fracture%20fa-Master.pdf - Photo 507 93-N-719 fracture face of the bungee cylinder attach bracket failure was 100 percent overload mag 61X (item 23, PDF, 1 page, 26 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467337&FileExtension=pdf&FileName=Photo%20507%20%2093-N-719%20Fracture%20face%20of%20the%20bungee%20cylinder%20attach%20bracket%20%20Failure%20was%20100%20percent%20overload%20%20Mag%2061-Master.pdf - Photo 508 93-N-715 overall view of the bungee springs these parts sustained no damage and met spring rate requiremen (item 24, PDF, 1 page, 27 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467339&FileExtension=pdf&FileName=Photo%20508%20%2093-N-715%20Overall%20view%20of%20the%20bungee%20springs%20%20These%20parts%20sustained%20no%20damage%20and%20met%20spring%20rate%20requi-Master.pdf - Photo 509 93-N-696 overall view of right side upper torque arm and pin view is looking outboard and forward mag (item 25, PDF, 1 page, 23 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467341&FileExtension=pdf&FileName=Photo%20509%20%2093-N-696%20%20Overall%20view%20of%20right%20side%20upper%20torque%20arm%20and%20pin%20%20View%20is%20looking%20outboard%20and%20forward%20%20M-Master.pdf - Photo 510 93-N-697 close-up of outer bushing of the right side upper torque arm note the damage indicative of late (item 26, PDF, 1 page, 32 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467343&FileExtension=pdf&FileName=Photo%20510%20%2093-N-697%20%20Close-up%20of%20outer%20bushing%20of%20the%20right%20side%20upper%20torque%20arm%20%20Note%20the%20damage%20indicative%20of-Master.pdf - Photo 511 93-N-698 close-up of inner bushing of the right side upper torque arm note that the bushing has been push (item 27, PDF, 1 page, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467345&FileExtension=pdf&FileName=Photo%20511%20%2093-N-698%20%20Close-up%20of%20inner%20bushing%20of%20the%20right%20side%20upper%20torque%20arm%20%20Note%20that%20the%20bushing%20has%20been-Master.pdf - Photo 512 93-N-800 rtv rubber mold made of the bushings shown in photos no 10 and 11 note circumferential cracking (item 28, PDF, 1 page, 29 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467347&FileExtension=pdf&FileName=Photo%20512%20%2093-N-800%20%20RTV%20rubber%20mold%20made%20of%20the%20bushings%20shown%20in%20photos%20No%2010%20and%2011%20%20Note%20circumferential%20crac-Master.pdf - Photo 513 93-N-687 overall view of apex bolt after removal from the right side shimming damper assembly note the st (item 29, PDF, 1 page, 23 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467349&FileExtension=pdf&FileName=Photo%20513%20%2093-N-687%20%20Overall%20view%20of%20Apex%20bolt%20after%20removal%20from%20the%20right%20side%20shimming%20damper%20assembly%20%20Note%20t-Master.pdf - Photo 514 93-N-688 close-up of the apex bolt photo 13 showing lines indicative of a straight-pull type of failure (item 30, PDF, 1 page, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467351&FileExtension=pdf&FileName=Photo%20514%20%2093-N-688%20%20Close-up%20of%20the%20Apex%20Bolt%20Photo%2013%20showing%20lines%20indicative%20of%20a%20straight-pull%20type%20of%20failu-Master.pdf - Photo 515 93-N-689 headstamp of the failed apex bolt identification is cpt 231 h t mag 24X (item 31, PDF, 1 page, 33 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467353&FileExtension=pdf&FileName=Photo%20515%20%2093-N-689%20%20Headstamp%20of%20the%20failed%20Apex%20bolt%20%20Identification%20is%20%20CPT%20231%20H%20T%20%20%20Mag%2024X-Master.pdf - Photo 516 93-N-694 photomacrograph of the right side apex bolt showing nickel plate on the shank extending to but n (item 32, PDF, 1 page, 41 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467355&FileExtension=pdf&FileName=Photo%20516%20%2093-N-694%20%20Photomacrograph%20of%20the%20right%20side%20Apex%20bolt%20showing%20nickel%20plate%20on%20the%20shank%20extending%20to%20b-Master.pdf - Photo 517 photomacrograph of the left side apex bolt showing nickel plate as in photo no 16 the plating thickness (item 33, PDF, 1 page, 41 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=1467357&FileExtension=pdf&FileName=Photo%20517%20%20Photomacrograph%20of%20the%20left%20side%20Apex%20bolt%20showing%20nickel%20plate%20as%20in%20Photo%20No%2016%20%20The%20plating%20thickne-Master.pdf - Applicable portions of ATC package-34 (item 34, PDF, 21 pages, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14956701&FileExtension=pdf&FileName=Applicable%20Portions%20of%20ATC%20Package-34-Master-Rel.pdf From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.