Selection Criteria - PSE

(1) The factors used to find the PSE's  include:

(a) Service Experience

1 Multiple sources of information were used to find the service discrepancies.

a Cessna Service Bulletins and Service Information Letters issued to repair common service discrepancies were examined.

b FAA Service Difficulty Records and Foreign certification agency Service Difficulty Records were examined.

2 Existing analyses were reviewed to identify components in areas that may have exhibited the potential for additional inspection requirements.

3 A review of test results applicable to the design was made to identify the critical areas of the PSE's.

3. Usage

A. Aircraft Usage

                      (1) Aircraft usage data for the SID program is based on the evaluation of the in-service utilization of the aircraft. This data was used to develop the representative fatigue loads spectra. Operational data for development of the Supplemental Structural Inspection Program was obtained from surveys of aircraft operators.

                     (2) Usage for spectra determination is defined in terms of a single flight representing typical average in-service utilization of the aircraft. This usage reflects the typical in-service flight variation of flight length, takeoff gross weight, payload and fuel.

                     (3) The flight is defined in detail in terms of a flight profile. The profile identifies the gross weight, payload, fuel, altitude, speed, distance etc., required to define the pertinent flight and ground parameters needed to develop the fatigue loads. The flight is then divided into operational segments, where each segment represents the average values of the parameters (speed, payload, fuel etc.) that are used to calculate the loads spectrum.

B. Stress Spectrum.

                  (1) A fatigue loads spectrum, in terms of gross area stress, was developed for each PSE to be analyzed based on the usage-flight profiles. The spectrum represents the following loading environments: flight loads (gust and maneuver), landing impact, taxi loads and ground-air-ground cycles. The resulting spectrum is a representative flight-by-flight, cycle-by-cycle loading sequence that reflects the appropriate and significant airplane response characteristics.

                (2) After reviewing the aircraft usage data and the way in which the surveyed aircraft were flown, two sets of stress spectra were developed. The first flight profile represents typical usage, while the second profile represents severe usage.

Repairs, Alterations and Modifications (RAM)

(1) Repairs, alterations and modifications (RAM) made to PSE's may affect the inspection times and methods presented in the SID. The flowchart in Figure 1 can be used to determine if a new assessment and FAA approved supplemental inspections are required.

(2) Repairs may be made in accordance with Section 17 of the Model 152 Service Manual or the REPAIR/MODIFICATION Section of the SID.

PSE Data Sheets

                                         

A data sheet for each PSE is provided in Section 2A-14-XX -

Each data sheet contains the following:

(1) Supplemental Inspection Number

(2) Title

(3) Effectivity

(4) Inspection Compliance

(5) Initial Inspection Interval(s)

(6) Repeat Inspection Interval(s)

(7) Purpose

(8) Inspection Instructions

(9) Access/Location/Zone

(10) Detectable Crack Size

(11) Inspection Procedure

(12) Repair/Modification

(13) Comments

NOTE: Inspection intervals are given in both hour and calendar time. After the completion of each initial SID inspection, repeat inspections may be completed based on hour time if the Corrosion Prevention and Control Program (CPCP) in Section 2A-30-00 is included in the airplane maintenance program.

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

Cessna 152 - PSE

Principal Structural Elements - Cessna 152

                 Description :An airplane component is classified as a Principal Structural Element  if:

(a) The component contributes significantly to carrying flight and ground loads.

(b) If the component fails, it can result in a catastrophic failure of the airframe.

               The monitoring of these PSE's is the main focus of this Supplemental Structural Inspection Program.

                           Typical Examples of Principal Structural Elements

Wing and Empennage:

Control surfaces, flaps and their mechanical systems and attachments (hinges, tracks and fittings)

Primary fittings

Principal splices

Skin or reinforcement around cutouts or discontinuities

Skin-stringer combinations

Spar caps

Spar webs

Fuselage:

Circumferential frames and adjacent skin

Door frames

Pilot window posts

Bulkheads

Skin and single frame or stiffener element around a cutout

Skin and/or skin splices under circumferential loads

Skin or skin splices under fore and aft loads

Skin around a cutout

Skin and stiffener combinations under fore-and-aft loads

Door skins, frames, and latches

Window frames

Landing Gear and Attachments

Engine Support Structure and Mounts

                                 

For Details: Cessna Maintenance Manual TR 05

http://aircraftmaintenanceindia.blogspot.in/2012/08/pse-principal-structural-elements.html

Principal Structural Elements

PSE - Principal Structural Elements 

              PSE’s are those elements of primary structure which contribute significantly to carrying flight, ground, and pressurization loads, and whose failure could result in catastrophic failure of the airplane.
             Engineering design and damage evaluation – repair criteria for aircraft structures are location dependent depending on whether the structure is considered and classified as either Primary, Secondary or as a PSE (Principal Structural Element).  
             Typically most aircraft structural repair manuals contain guidance through charts or diagrams that define what parts of the aircraft  are classified as Principal Structural Elements – PSE’s, Primary or Secondary structure.
             Additionally, virtually all repairs (other than straight parts replacement) on transport aircraft to Principal Structural Elements or Primary structures are classified as Major Repairs thus necessitating the use of Approved rather than Accepted data to accomplish the repair. This rule should be considered the minimum requirement since some regulatory organizations are more restrictive than the others.

Examples of Principal Structural Elements typically include:

(1) Wing and empennage.

(a) Control surfaces, slats, flaps, and their mechanical systems and attachments (hinges, tracks, and fittings);

(b) Integrally stiffened plates;

(c) Primary fittings;

(d) Principal splices;

(e) Skin or reinforcement around cutouts or discontinuities;

(f) Skin-stringer combinations;

(g) Spar caps; and

(h) Spar webs.

(2) Fuselage.

(a) Circumferential frames and adjacent skin;

(b) Door frames;

(c) Pilot-window posts;

(d) Pressure bulkheads;

(e) Skin and any single frame or stiffener element around a cutout;

(f) Skin or skin splices, or both, under circumferential loads;

(g) Skin or skin splices, or both, under fore and aft loads;

(h) Skin around a cutout;

(i) Skin and stiffener combinations under fore and aft loads;

(j) Door skins, frames, and latches; and

(k) Window frames.

(3) Landing gear and their attachments.

(4) Engine mounts.