# NTSB GAA16CA487: Cessna 172, N52950, Anchorage, AK, September 1, 2016 - Type: NTSB accident investigation - Classification: Accident · No injuries · Data collection · Final report - Date: September 1, 2016, 13:12 local (21:12 UTC) - Place: Anchorage, AK - Coordinates: 61.213054, -149.839996 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=61.2131&lon=-149.8400&mi=10 - Phase of flight: [Taxi](https://openairdocs.org/ntsb-phases/250) (OpenAirDocs' grouping) - Defining event: [Taxi-to runway: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report January 18, 2017 - Report: Approved by Office Director - NTSB office: General Aviation Accidents - Parties: FAA - NTSB case key (mKey): 94014 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=GAA16CA487 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/94014/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=94014 - Page: https://openairdocs.org/ntsb/GAA16CA487 ## Probable cause The airplane’s encounter with a developing sink hole during taxi on the ramp area. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Runway/land/takeoff/taxi surface](https://openairdocs.org/ntsb-findings/03023000): Environmental issues › Physical environment · Effect on equipment (probable cause); cases with it: [Cessna 172P, 2 cases](https://openairdocs.org/ntsb-findings/03023000/cases.md?model=2072436), [All aircraft, 253 cases](https://openairdocs.org/ntsb-findings/03023000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Taxi-to runway: Miscellaneous/other](https://openairdocs.org/ntsb-events/900) (defining event); cases with it: [Cessna 172P, 6 cases](https://openairdocs.org/ntsb-events/900/sequence.md?model=2072436), [All aircraft, 1,556 cases](https://openairdocs.org/ntsb-events/900/sequence.md) ## Analysis The flight instructor reported that during taxi the airplane started to lean to the right, so he looked out of his window to see if the right tire was flat. He further reported that "the ramp was opening up into a 2 foot wide dark black hole" underneath the right main landing gear. The flight instructor and student pilot egressed from the airplane without further incident. A postaccident examination revealed substantial damage to the empennage. The flight instructor reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. Photographs provided by Federal Aviation Administration showed that the right main landing gear had broken through the pavement into a sink hole underneath. ## Factual narrative The flight instructor reported that during taxi the airplane started to lean to the right, so he looked out of his window to see if the right tire was flat. He further reported that "the ramp was opening up into a 2 foot wide dark black hole" underneath the right main landing gear. The flight instructor and student pilot egressed from the airplane without further incident. A postaccident examination revealed substantial damage to the empennage. The flight instructor reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. Photographs provided by Federal Aviation Administration showed that the right main landing gear had broken through the pavement into a sink hole underneath. ## Aircraft - Registration: [N52950](https://openairdocs.org/aircraft/N52950), registered now, S/N 17274642, built 1981 (OpenAirDocs) - Reported make and model: CESSNA 172 (P) - Registry model: [Cessna 172P](https://openairdocs.org/model/cessna-172p) (registry code 2072436) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 17274642 - Year built: 1981 - Engines: LYCOMING O-320 180 horsepower reciprocating - Damage: Substantial damage - Flight: Instructional, Part 91 - Operator: Land and Sea Aviation Alaska - Registered owner: Flight Safety Alaska Inc - Airworthiness certificate: Standard, Normal - Last inspection: Annual, August 19, 2016 - Departed: MRI, Anchorage, AK - Destination: MRI, Anchorage, AK - Airport: MRI, Merrill Field - Equipment: Stall warning system ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 33; injuries: none; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, without waivers/limitations; last flight review May 1, 2015; seat: right; restraint: 3-point; flight hours: 967 total, 600 in this make and model - Student pilot; age 31; injuries: none; student; medical: class 3, without waivers/limitations; seat: left; restraint: 3-point; flight hours: 10 total, 10 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 20° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: 6,500 ft overcast - Temperature: 66 °F, dew point 54 °F - Altimeter: 30.02 inHg - Observed at: PAMR ## 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 20160901022949A](https://openairdocs.org/incident/20160901022949A), Sep 1, 2016: Cessna 172P, Anchorage, AK, Substantial damage. On 1 sep, 2016, my student and I put the flaps up in N52950, while sitting on a taxiway near to abeam the land and sea aviation fuel point, getting ready to… ## Docket (2 files) The files NTSB released with the investigation on December 12, 2016, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=94014. 553 KB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 257 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40458991&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Accident Photos (item 2, .PDF, 296 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40447385&FileExtension=.PDF&FileName=Accident%20Photos-Master.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.