# NTSB LAX94LA163: Rockwell 681, N78CH, Phoenix, AZ, March 13, 1994 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: March 12, 1994, 23:20 local (Mar 13, 1994, 06:20 UTC) - Place: Phoenix, AZ - Coordinates: 33.679103, -112.090492 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=33.6791&lon=-112.0905&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 5 uninjured - Status: Completed, report November 18, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 28697 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX94LA163 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/28697/pdf - Page: https://openairdocs.org/ntsb/LAX94LA163 ## Probable cause the failure of the hydraulic and nitrogen system pressure lines, due to an inadequate maintenance inspection program, which failed to detect the corrosion condition of the lines. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - vfr pattern - final approach - hydraulic system,line - corroded (cause) - landing gear,emergency extension assembly - corroded (cause) - maintenance,inspection - inadequate, company maintenance personnel (cause) - hydraulic system - no pressure (cause) - landing gear,emergency extension assembly - no pressure (cause) - gear extension - not possible, pilot in command - Main gear collapsed, landing - flare/touchdown ## Analysis The pilot moved the landing gear selector switch to the down position; however, the landing gear did not extend. The pilot used the emergency gear down system; however, both main landing gear extended only partially and the main wheels failed to rotate to the streamlined position. The main gear collapsed on landing, resulting in damage to the lower fuselage bulkheads and gear attach structure. No hydraulic fluid was found in the system lines, and no leaks detected around the landing gear wells. The nitrogen system pressure was measured at 50 psi; the normal system pressure is 425 to 525 psi. Review of the hydraulic system lines revealed a metal line ruptured with hydraulic fluid saturating the immediate area. The maintenance records indicated the ruptured line was an original equipment item and at least 24 years old. A leak was found in the nitrogen system lines in the wing center section crossover line. Corrosion pitting was observed in several places on both of the lines. ## Factual narrative On March 12, 1994, at 2320 mountain standard time, a Rockwell 681, N78CH, sustained substantial structural damage during landing with the main gear partially extended at Phoenix, Arizona. The aircraft was operated by American Corporate Aviation, Inc., of Houston, Texas, and was engaged in air ambulance flight operations under the provisions of 14 CFR 135. The aircraft incurred substantial damage. The certificated airline transport pilot, the two flight nurses, and the two passengers were not injured. The flight originated at Show Low, Arizona, on the day of the mishap at 2230 hours as an aeromedical evacuation flight to Phoenix. According to the pilot's statement, while inbound to Phoenix he moved the landing gear selector switch to the down position; however, the landing gear did not extend. The pilot used the emergency gear down system, which consists of using pressurized nitrogen to force the landing gear down. The pilot reported that the nose gear extended; however, both main landing gear extended only partially and the main wheels failed to rotate to the streamlined position. Subsequent attempts to fully extend the main gear were unsuccessful. The aircraft landed and the main gear collapsed, resulting in damage to the lower fuselage bulkheads and gear attach structure. A Federal Aviation Administration (FAA) airworthiness inspector from the Scottsdale, Arizona, Flight Standards District Office examined the aircraft. He found no hydraulic fluid in the system lines, and no evidence of hydraulic fluid sprayed around the landing gear wells. The nitrogen system pressure was measured at 50 psi; according to the maintenance manual for the aircraft, the normal system charge pressure is 425 to 525 psi. Detailed examination of the hydraulic system lines revealed a 1/4-inch metal line ruptured at a point under the rear bench cabin seat. Hydraulic fluid saturated the immediate area. Corrosion pits were observed on the line in many places. The inspector reported that the maintenance records indicated the ruptured line was an original equipment item installed at aircraft manufacture on or before January 26, 1970. Examination of the nitrogen system lines revealed a leak in the wing center section crossover line. Corrosion pitting was observed in several places on the line. ## Aircraft - Registration: [N78CH](https://openairdocs.org/deregistered/N78CH-2014-10-14), registration cancelled 2014-10-14, S/N 6038, built 1970 (OpenAirDocs) - Reported make and model: ROCKWELL 681 - Registry model: [Aero Commander 681](https://openairdocs.org/model/aero-commander-681) (registry code 0141718) (OpenAirDocs) - Registry engine: [AiResearch 331 SER 605HP](https://openairdocs.org/engine/airesearch-331-ser-605hp) (registry code 01502, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 6038 - Airframe hours: 4424 - Engines: GARRETT TPE 331-151K 575 horsepower turbo prop - Damage: Substantial damage - Flight: Part 135 - Operator: American Corp Aviation - Registered owner: C&R Flying Service, Inc. - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, October 26, 1993, 96 hours before - Departed: SOW, SHOW LOW, AZ - Flight plan: IFR - Airport: PHX, Phoenix Sky Harbor Int., runway 26R, 11,001 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 31; airline transport, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 5,800 total, 275 in this make and model, 5,200 as pilot in command, 60 in the last 90 days, 25 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Night/dark - Visibility: 70 statute miles - Lowest ceiling: none ## 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 19940312005079A](https://openairdocs.org/incident/19940312005079A), Mar 12, 1994: Gulstm 681, Phoenix, AZ, Substantial damage. EMS flight landed with gear partial down. Hydraulic system empty. Fluid leak under rear seat. Line corroded pitted. 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.