Individually Owned: 150,657
Corporate Owned: 137,281
Phoenix Sky Harbor Intl. Airport
Aircraft Accident/Incident Report
Phoenix (Phx), Arizona 85034
Friday, June 27, 2008
NTSB Narrative Summary Released at Completion of Accident
In June 2008, after the incident airplane was towed, ground personnel noted that the left hand (LH) main landing gear (MLG) was leaking shock strut fluid from a crack in the wall of the outer cylinder. A visual examination of the outer cylinder revealed a crack located approximately 26” below the shock strut air valve. The outer cylinder had accomplished 3 ground air ground (GAG) cycles after completion of the December 2007 overhaul, and approximately 5836 cycles since the prior overhaul in 2004.
The subject outer cylinder developed fatigue cracking in the wall which resulted in leakage of shock strut fluid. The fatigue cracking initiated at and near the ID surface, and propagated through the wall toward to OD until the leakage was detected and the cylinder was removed from service. Crack initiation was due to base metal damage which took the form of over tempered martensite and chemical attack/pitting. The over tempering reduced the strength of the material and caused reduction of shot peen induced residual compressive stresses. The combination of these factors results in the affected material having reduced resistance to fatigue cracking. The ID surface displayed base metal chemical attack which most likely developed during a plating operation on the sealing surface during the 2004 overhaul. The pitting features act as stress raisers, thereby serving as favorable crack initiation sites. The observed ID surface conditions appear to have been created during the overhaul in 2004, with the fatigue cracking occurring once the cylinder was returned to service. The cracking in the cylinder wall was not detected during the 2007 overhaul. Spectrochemical analysis and hardness testing confirmed that the cylinder was fabricated from the specified material, in the required heat treat condition. The cylinder exhibited slightly elevated bulk hydrogen levels, likely caused by the multiple plating and stripping operations during the 2004 overhaul. The condition may have provided a minor contribution to the propagation of the fatigue crack after initiation had occurred.
NTSB Probable Cause Narrative
The failure of the MLG was due to cracking in the cylinder wall resulting from a fatigue mechanism which initiated at, and near the inner diameter (ID) surface, with propagation through the wall toward the outer diameter(OD) surface. Crack initiation was due to base metal damage which took the form of over tempered martensite (OTM) and chemical attack/pitting of the base metal.
Event Information
| Type of Event | Incident |
| Event Date | 6/27/2008 |
| Event Day of the Week | Friday |
| Time of Event | -- |
| Event Time Zone | -- |
| Event City | Phoenix (PHX) |
| Event State | ARIZONA |
| Event Country | -- |
| Zipcode of the event site | 85034 |
| Event Date Year | 2008 |
| Event Date Month | 6 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | 332604N |
| Event Location Longitude | 1120041W |
| Event Location Airport | Phoenix Sky Harbor Intl. |
| Event Location Nearest Airport ID | PHX |
| Indicates whether the acc/inc occurred off or on an airport | On Airport |
| Distance from airport in statute miles | -- |
| Degrees magnetic from airport | -- |
| Airport Elevation | 1135 |
| Weather Briefing Completeness | -- |
| Investigator's weather source | Unknown |
| Time of the weather observation | |
| Direction of event from weather observation facility (degrees) | -- |
| Weather Observation Facility ID | -- |
| Elevation of weather observation facility | -- |
| Distance of event from weather observation facility (units?) | -- |
| Time Zone of the weather observation | -- |
| Lighting Conditions | -- |
| Lowest Ceiling Height | -- |
| Lowest Non-Ceiling Height | -- |
| Sky/Lowest/Cloud Conditions | -- |
| Sky Condition for Lowest Ceiling | -- |
| Visibility Runway Visual Range (Feet) | -- |
| Visibility Runway Visual Value (Statute Miles) | -- |
| Visibility (Statute Miles) | -- |
| Air Temperature at event time (in degrees celsius) | -- |
| Dew Point at event time (in degress fahrenheit) | -- |
| Wind Direction (degrees magnetic) | -- |
| Variable Wind Indicator | -- |
| Wind Speed (knots) | -- |
| Wind Velocity Indicator | -- |
| Wind Gust Indicator | -- |
| Wind Gust (knots) | -- |
| Altimeter Setting at event time (in. Hg) | -- |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | -- |
| METAR weather report | -- |
| Event Highest Injury | -- |
| On Ground, Fatal Injuries | 0 |
| On Ground, Minor Injuries | 0 |
| On Ground, Serious Injuries | 0 |
| Injury Total Fatal | -- |
| Injury Total Minor | -- |
| Injury Total None | -- |
| Injury Total Serious | -- |
| Injury Total All | -- |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 28208 |
| NTSB Notification Source | Federal Aviation Administratio |
| NTSB Notification Date | -- |
| NTSB Notification Time | -- |
| Fiche Number and/or location -used to find docket information | -- |
| Date of most recent change to record | Mar 31 2011 11:53AM |
| User who most recently changed record | murb |
| Basic weather conditions | -- |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N514AU |
| NTSB Number | ENG08IA051 |
| Missing Aircraft Indicator | -- |
| Federal Aviation Reg. Part | Part 121: Air Carrier |
| Type of Flight Plan filed | None |
| Flight plan Was Activated? | No |
| Damage | Minor |
| Aircraft Fire | None |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | BOEING |
| Aircraft Model | 737 |
| Aircraft Series Identifier | 3B7 |
| Aircraft Serial Number | 23700 |
| Certified Max Gross Weight | 138500 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | -- |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | 126 |
| Total number of seats on the aircraft | -- |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Unknown |
| Date of Last Inspection | -- |
| Airframe hours since last inspection | -- |
| Airframe Hours | -- |
| ELT Installed | Unknown |
| ELT Activated | Unknown |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | 737 PORTFOLIO TRUST |
| Aircraft Owner Street Address | 1100 N MARKET ST |
| Aircraft Owner City | WILMINGTON |
| Aircraft Owner State | DE |
| Aircraft Owner Country | USA |
| Aircraft Owner Zipcode | 19890 |
| Operator is an individual? | No |
| Operator Name | US AIRWAYS INC |
| Operator Same as Owner? | No |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | No |
| Operator Street Address | 4000 Sky Harbor |
| Operator City | Phoenix |
| Operator State | AZ |
| Operator Country | USA |
| Operator Zip code | 85034 |
| Operator Code | USAA |
| Owner has at least one certificate | Yes - certificate holder |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | -- |
| Operator Certificate Number | USAA105A |
| Indicates whether an air carrier operation was scheduled or not | Scheduled |
| Indicates Domestic or International Flight | Domestic |
| Operator carrying Pax/Cargo/Mail | Passenger Only |
| Type of Flying (Per_Bus / Primary) | -- |
| Second Pilot on Board | No |
| Departure Point Same as Event | Yes |
| Departure Airport Code | -- |
| Departure City | -- |
| Departure State | -- |
| Departure Country | USA |
| Departure Time | -- |
| Departure Time Zone | -- |
| Destination Same as Local Flt | crash at destination city |
| Destination Airport Code | -- |
| Destination City | -- |
| Destination State | -- |
| Destination Country | USA |
| Specific Phase of Flight | -- |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Nov 17 2010 2:07PM |
| User who most recently changed record | murb |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | N/A |
| Runway Length | -- |
| Runway Width | -- |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |