Fatigue Assessment

Cessna 152 SSIP

               (1) The fatigue assessment provides the basis for establishing inspection frequency requirements for each PSE. The evaluation includes a determination of the probable location and modes of damage and is based on analytical results, available test data and service experience. In the analysis, particular attention is given to potential structural condition areas associated with aging aircraft. Examples include:

                      (a) large areas of structure working at the same stress level, which could develop widespread fatigue damage;

                      (b) a number of small (less than detectable size) adjacent cracks suddenly joining into a long crack (e.g. as in a line of rivet holes);

                     (c) redistribution of load from adjacent failing or failed parts causing accelerated damage of nearby parts (i.e., the “domino" effect); and

                    (d) concurrent failure of multiple load path structure (e.g. crack arrest structure).

               (2) Initial inspections of a particular area of structure are based on fatigue analytical results. For locations with long fatigue the maximum initial inspection was limited to 12,000 flight hours.

D. Classifications for Types of Operation

              (1) The severity of the operation environment needs to be identified to determine the correct inspection program.

                      (a) You must first find the category of your airplane’s operation based on average flight length.

                     (b) You must also find the number of hours and number of landings on the airplane, then find the average flight length based on the formula found below.

Average Flight Length = Number of Flight Hours / Number of Flights

              (2) If the average flight length is less than 30 minutes, then you must use the SEVERE inspection time limits. For airplanes with an average flight length greater than thirty minutes, you must find the severity of the operating environment.

             (3) Airplanes which have engaged in operations at low altitudes such as pipeline patrol, fish or game spotting, aerial applications, police patrol, sightseeing, livestock management etc. more than 30% of its life must use the SEVERE inspection time limits.

             (4) For all other operating environments, inspections should be conducted using the TYPICAL Inspection Time Limits.

Corrosion Severity

(1) Prior to conducting the initial corrosion inspection, determine where the airplane has resided throughout its life. If the airplane has resided in a severe corrosion environment for 30% or more of the years to the initial inspection, use the severeinspection time, otherwise use the mild/moderate inspection time.

(2) Prior to conducting a repetitive corrosion inspection, determine where the airplane has resided since the last inspection. If the airplane has resided in a severe environment for 30% or more of the years since the last inspection, use the severe inspection time, otherwise use the mild/moderate inspection time