Phases of Aircraft Certification

1.  Certification

           Certification is defined as a process that provides the possibility of making certain that any aircraft, whether civil or military, has acceptable levels of safety for a given future utilization within the defined flight load spectrum for a specified period.

2.   Phases of Certification of an Aircraft

          Certification is normally carried out in four levels as shown in Figure - 1 below:

Figure -1: Aircraft Certification Phases

a) Level 1: Requirement Finalization - The requirement of the aircraft or the technical specification, the design standards (like FAR, MIL, etc.), and the materials to be used (existing approved materials or new materials to be developed) are decided in this phase. 

b)  Equipment (LRU) and Component Qualification 

c) System-level Qualification, and 

d) Aircraft level functionality and operability assessment.  

3.  LRU Qualification 

     The LRU (Line Replaceable Units) development and Qualifications are carried out in phases as follows:

a) Development of F-F-F Model (Form, Fit and Function) - It is a model unit and used for checking the installation, functioning, and access for maintenance. 

b) Prototype Model - Based on the F-F-F model experience, a prototype model is built with the engineering material to check proper functioning in the full environment. 

c) SOFT Model - SOFT (Safety of Flight Test) model is a model that is subjected to all those exposure tests that are felt in each flight. SOFT is a subset of QT (Qualification Test), and SOFT-cleared items can be released for developmental flight trials. In parallel, full QT is carried out on other models. 

d) Qualification Test  (QT) Model - The QT model is subjected to qualification tests as follows;

     - Functional test on the test rig

     - Structural test as proof of structural integrity

     - System Integration and ground evaluation 

     - Environmental test 

     - Flight and ground test 

     - Endurance test for life cycle environment. 

Note: Qualification tests may be spread across different prototype samples as shown below: 

        1) Sample 1 - Full Range of Structural Integrity and functional tests.

        2) Sample 2 - After the quality acceptance test, the prototype is subjected to the full life or                            Endurance test. 

       3) Sample  3 - Full exposure to environmental tests (Salt, fog, fungus growth, etc.)

4.  System Level Certification 

An aircraft comprises many systems like airframe structure, mechanical, electrical, powerplant, and avionics. The configuration design is based on aerodynamic considerations. The system-level certification will consist of the evaluation of the system: 

  - System-level functional requirements under all environments

  -  System safety and hazard requirements as per airworthiness standards

  - System Reliability (Redundancy or Fault tolerance) requirements 

  -  Maintainability requirements and 

  -  Specified life 

System evaluations go in phases

 - Design evaluation as per airworthiness standards/regulations

 - Functional evaluation on the system integration rig/box

 - Performance evaluation on "Aircraft on Ground" test (initially with ground power supply and later         with aircraft's own power (engine running)) 

 - Performance evaluation on aircraft during flight.

5. Aircraft Level Evaluation 

Aircraft-level tests to verify each system's functioning at various stages:  

  - System evaluation during engine ground run (EGR)

  - System evaluation during Low Speed Taxi Test (LSTT) (speed limited to 50 knots) 

  - System evaluation during High Speed Taxi Test (HSTT) (speed limited below to Vrotation speed)

  - Flight test evaluation 

6. Flight Test and Evaluation 

The principal purpose of flight testing is to determine if the complex machine designed can safely accomplish the designated task with the pilot workload kept within the human limitations and natural instinct of human beings.

The flight test includes handling quality assessment and evaluation of airworthiness performance, as well as all mission performance requirements. The flight tests are also to establish the operational boundary of the aircraft, aero-elastic and other boundaries. The all weather assessment will involve tests and evaluations under various airport altitude and ambient conditions. 

All weather clearance tests include high altitude, operations under extreme temperatures, as well as rainwater leak tests, and night flying tests.  

However, there are some hazardous tests like determination of stall and spin behaviours, engine relight in air, safety assessment during simulated system failures, etc., which are normally carried out only after gathering enough data on the aircraft behaviour through flight tests. 

Military aircraft also need to go through weapon firing trials. 

7. Certification 

Based on the satisfactory tests and evaluation aircraft is issued with 

  - Type Certification (Civil Aircraft) 

  - Military Type Certificate (MTC) and Induction to service (Military aircraft). For the induction to

    service, an RSD (Release to Service Document), approved by CEMILAC, is issued. 

Associated activity during the certification stage is the preparation of ODM (Operational Data Manual), AFM (Aircraft Flight Manual) and MM (Maintenance manuals).