The concern sheet
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Airworthiness Concern Sheet
Gary D. Park Aerospace Engineer Wichita Aircraft Certification Office ACE-118W 1801 Airport RD Wichita, KS 67209 316-946-4123 Gary.Park@faa.gov Make, Model, Series, Serial No.: Cessna Models 120, 140, 150, 170, 172, 175, 180, 182, 185, 188, 190, 195, 205, 206, 210 Reason for Airworthiness Concern: Corrosion and fatigue cracking of the main landing gear (MLG) spring struts have caused MLG failures on various Cessna airplane models.
FAA Description of Airworthiness Concern The left MLG broke on a 172K that did a ground loop on June 18, 2007. On May 6, 2006, the left MLG leg broke off at 4 inches from the axle attach point on an A185F. Both of these failures were due to corrosion/fatigue. Our records indicate 72 occurrences beginning in 1975 until the present time. Of these 72, 35 were identified as being axle and hardware failures; and 37 as being spring strut failures. Our analysis of the SDR and accident data indicate that, for the axle and hardware failures, the number of SDRs per year has dropped from 3.3 (1974 to 1981) to 1.0 since 1981; for the spring strut, the number of SDRs per year has increased from 0.6 (1974 to 1987) to 1.4 since 1987. We have reason to believe that wearout for the spring struts is about 3000 flight hours on rough terrain, and about 8000 flight hours on paved runways. At this time, we believe that our analysis is showing that these spring struts should be visual and NDI inspected every 2000 flight hours. The axle and hardware should be at least visually inspected every 2000 flight hours.
In 2001, the NTSB issued two safety recommendations: The first recommended an initial inspection at the next 100-hour or annual inspection; and the second recommended repetitive inspections at appropriate intervals.
At this time, the FAA has not made a determination on what type of corrective action (if any) should be taken. The resolution of this airworthiness concern could involve an Airworthiness Directive (AD) action or a Special Airworthiness Information Bulletin (SAIB), or the FAA could determine that no action is needed at this time. The initial Risk Assessment for this concern indicated that an AD or SAIB might be considered.
Enclosed are: (1) the Initial Risk Assessment Evaluation Chart (IRAEC), (2) a photograph of the latest failure, (3) the previous ACS dated 5/23/01, (4) FAA AC43-16A article dated July 2002, (5) a schematic of a spring strut, and (6) Cessna temporary revision to their service manual.
Comments The FAA requests your comments.
Note: Any comments or replies to the FAA need to be as specific as possible. Please provide specific examples to illustrate your comments/concerns.
Date: September 20, 2007 Attachments: *SDR(s) *A/IDS *SL(s) *SAIB *FAASR/*NTSBSR *AD *AMOC *RA
Notification: FAA *AOPA *EAA Type Club *TC Holder Other: GAMA
Response Requested 10/29/07: Emergency (10 days) Alert (30 days) Information (90 days) (Space Bar Adds “X” to Check Boxes) *Service Difficulty Reports (SDRs); Accident/Incident Data System (A/IDS); Service Letter (SL); Special Airworthiness Information Bulletin (SAIB);
Federal Aviation Administration (FAA)/National Transportation Safety Board (NTSB) Safety Recommendation (FAASR/NTSBSR); Airworthiness Directive (AD); Alternate Method of Compliance (AMOC); Risk Assessment (RA); Aircraft Owners & Pilots Association (AOPA);
Experimental Aircraft Association (EAA); Type Certificate (TC)
10 20 30 40 50 Catastrophic (4) (Loss of Aircraft/ Multiple Fatalities) Safety Effect Minor (1) (Slight Reduction in Safety Margins, Increase in Workload) Major (2) (Significant Workload Increase, Possible Injury/Death Hazardous (3) (Large reduction in capabilities, serious or fatal injuries) Potential Company Service Information, General Aviation Alert or Special Airworthiness Information Bulletin (SAIB) (Incident/Voluntary Inspections (Notify Public)) Potential Routine AD (Potential Notice For Proposed Rulemaking (NPRM) AD) (Corrective Action/Mandatory Inspections/Modifications May be Needed) Urgent Safety of Flight Situation (Potential (Immediate) Adopted Final Rule AD with comments requested or Potential Final Rule after Notice) (Timely Corrective Action/Mandatory Inspections/Mods May be Needed)
Urgent Safety of Flight Situation (Potential Emergency AD Action)
Initial Risk Assessment Evaluation Chart (IRAEC) (See Safety Effect), reference 2.1) Safety Risk Factor (reference 2.1.1 & 3.1) Figure 1 Note: This chart is not intended to mandate A/W corrective actions, but is intended to supplement the decision-making process.
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