# NTSB ANC93IA085: Piper PA-31-350, N3588Z, King Salmon, AK, May 26, 1993 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: May 26, 1993, 15:30 local (23:30 UTC) - Place: King Salmon, AK - Coordinates: 58.75069, -156.540222 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=58.7507&lon=-156.5402&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report December 19, 1994 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 2320 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC93IA085 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/2320/pdf - Page: https://openairdocs.org/ntsb/ANC93IA085 ## Probable cause THE FAILURE OF THE MAIN GEAR UPPER STRUT ASSEMBLY DUE TO STRESS CORROSION. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Main gear collapsed, landing - roll - landing gear,main gear strut - stress corrosion (cause) ## Analysis THE RIGHT MAIN GEAR UPPER STRUT ASSEMBLY SEPARATED ON LANDING. METALLURGICAL EXAMINATION SHOWED THAT THE STRUT ASSEMBLY FAILED DUE TO STRESS CORROSION CRACKS OCCURRING ACROSS THE FORGED PARTING PLANE. ## Factual narrative On May 26, 1993, at 1530 Alaska daylight time, a retractable gear, wheel equipped Piper PA-31-350, Navajo airplane, N3588Z, registered to and operated by Peninsula Airways, Inc. of Anchorage, Alaska, experienced a right main gear collapse during landing at King Salmon, Alaska. The positioning flight, operating under 14 CFR Part 91, last departed Chignik, Alaska, and the destination was King Salmon. The Airline Transport Certificated Pilot-in-Command, the sole occupant, was not injured, and the airplane received only minor damage. Visual meteorological conditions prevailed and a company flight plan was in effect. Examination of the airplane showed that the right main landing gear strut housing had separated into 4 major pieces. The pieces were submitted for metallurgical examination and the results revealed the following information. The strut housing was made from 2014-T6 aluminum alloy which can be susceptible to stress corrosion cracking if it is exposed to halogens, such as fluoride, chloride, etc., in aqueous solutions and is assisted by either external or internal applied stress. The metallurgical examination determined that isolated areas of corrosion that emanated from the outer diameter of the strut housing assembly along the forge parting plane was caused by a chloride contaminant. The metallurgical report further stated that: "Branch cracking and intergranular cracks are indicative of stress-corrosion cracking in aluminum alloys. Although branch cracking was not noted in the metallurgical sections, intergranular cracks were observed on the fractures in section "1-1" (of the attached metallurgical report) to suffice that intergranular cracking was the preferred corrosion mechanism that caused separation of the strut housing." Furthermore, the metallurgical report stated that another factor which assisted in the separation of the strut housing assembly was the perpendicular stress applied to the forge parting plane. "It is believed that the strut housing assembly was subjected to such a stress when the main landing gear touched the ground causing the pre-existing stress-corrosion cracks to propagate rapidly through he forging parting plane and the assembly to separate." According to the State of Alaska, none of the state owned airports use a chloride-based solution for sanding runways, taxiways, or roadways in close proximity to runways and/or taxiways. The military installations use either UREA or glycol in the sand. Examination of the environment in which the airplane operations, the Aleutian Chain, shows that it is surrounded by salt water and is subjected to high winds. An example given was Dutch Harbor, Alaska, where the ocean spray and waves obliterate the ends of the runway on a regular basis. The airplane is operated consistently on the Aleutian Chain, including Dutch Harbor. ## Aircraft - Registration: [N3588Z](https://openairdocs.org/deregistered/N3588Z-2005-05-10), registration cancelled 2005-05-10, S/N 31-8052130, built 1980 (OpenAirDocs) - Reported make and model: PIPER PA-31-350 - Registry model: [Piper PA-31-350](https://openairdocs.org/model/piper-pa-31-350) (registry code 7103110) (OpenAirDocs) - Registry engine: [Lycoming TI0-540 series](https://openairdocs.org/engine/lycoming-ti0-540-series) (registry code 41533, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 31-8052130 - Airframe hours: 4317 - Engines: LYCOMING TIO-540-J2BD 350 horsepower reciprocating - Damage: Minor damage - Flight: Part 91 - Operator: Peninsula Airways, Inc., doing business as Penair - Registered owner: Peninsula Airways, Inc. - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, April 30, 1993, 85 hours before - Departed: KCG, CHIGNIK, AK - Flight plan: Company VFR - Airport: AKN, King Salmon, runway 11, 8,500 × 150 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 42; airline transport; airplane ratings: multi-engine land, single-engine land, multi-engine sea; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 10,700 total, 1,100 in this make and model, 10,500 as pilot in command, 220 in the last 90 days, 60 in the last 30 days, 4 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 150° at 15 knots, gusting 19 - Visibility: 30 statute miles - Lowest ceiling: none - Temperature: 55 °F, dew point -0 °F ## 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 19930526019839A](https://openairdocs.org/incident/19930526019839A), May 26, 1993: Piper PA31350, King Salmon, AK, Minor damage. Right main landing gear collapsed landing. Fatigue cracks from salt water spray and repetive over stress landings. ## Other investigations on N3588Z (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 ANC95LA050](https://openairdocs.org/ntsb/ANC95LA050), May 8, 1995: Piper PA-31-350 (N3588Z), Dillingham, AK, substantial damage. Probable cause: THE PILOT'S INADEQUATE PREFLIGHT PLANNING AND PREPARATION. FACTORS ASSOCIATED WITH THE ACCIDENT ARE: THE DISPATCHER'S DECISION TO DISPATCH A MULTI-ENGINED AIRPLANE TO A SHORT, SOFT AIRSTRIP, AND… 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.