China CAAC Regs and Procedures: Modification Design Approval (MDA) Part 1

13 June 2017
13 June 2017, Comments: 0

In China, some modifications will require an MDA rather than a VSTC.

Note: While all information given below is believed to be accurate at the time of writing, this post only intends to provide a general overview. Please contact us for the latest information and advice.

For all imported aircraft, where major modifications not covered by an STC issued by the airworthiness authorities of the country of origin are to be carried out, a CAAC-issued Modification Design Approval (MDA) is required.

1. Regulatory Background


CAAC-issued AP-21-15 “Major Modification Design Certification Procedures for Imported Civil Aircraft” is based on CCAR-21 “Approval Regulations for Civil Aircraft Parts.” The AP applies to major modifications of imported civil aircraft registered in China, including major modifications to the airframes, engines, propellers, airborne equipment, and so on.

Those modifications that:

  1. may significantly affect the weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other airworthiness characteristics of an aircraft, or
  2. are not carried out in accordance with accepted routine practices or basic methods of operation;

are major modifications.


In CCAR-43 we also find the following definition:

Those modifications that are not included in the design specifications of the aircraft or parts manufacturers, and may have significant influence on the weight, balance, strength, performance, dynamic characteristics, flight characteristics and other factors of airworthiness, or cannot be completed by accepted routine methods or  basic operations, can be regarded as major modifications.

2. MDA vs STC

For all imported aircraft, engines and propellers, if the modification is to be carried out under an STC issued by the country of origin’s airworthiness authorities, then it is necessary to apply to the CAAC for a Validation of Supplemental Type Certificate (VSTC). Otherwise, a Modification Design Approval (MDA) from the CAAC must be obtained.

CAAC-issued STCs are reserved for domestically produced aircraft only.

The following table summarizes the major differences between a VSTC and an MDA:



Aircraft origin Imported Imported
VTC required? Yes Yes
Modification in accordance with STC from country of origin? Yes No
Who may apply? Holder of STC issued in country of origin only Various legal persons (see Part 2)
Recognized by other authorities? Yes No

3. Classification

The classification of types of major modifications is basically the same as that of other major airworthiness jurisdictions such as the FAA:

Airframe major modifications

Modifications to the following parts and modifications of the following type, when not listed in CAAC approved aircraft technical data, are airframe major modifications:

  • Wings
  • Tail Surfaces
  • Fuselage
  • Engine mounts
  • Control system
  • Landing Gear
  • Hull or Floats
  • Airframe components including spars, ribs, fittings, shock absorbers, struts, engine cowlings, fairings, and mass-balance weights.
  • Hydraulic or electrical actuators
  • Rotor blades
  • Changes to the empty weight or empty balance which result in an increase in the maximum certificated weight or center of gravity limits of the aircraft.
  • Alterations to the basic design of systems such as fuel, oil, heating, cooling, pressurization, electrical, hydraulic, deicing or exhaust
  • Changes to wing structure or fixed/movable control surfaces which affect flutter and vibration characteristics.
Powerplant Major Modifications

Modifications to powerplants listed below, when not listed in CAAC approved aircraft technical data, are powerplant major modifications:

  • Alterations to engine type, including any changes in compression ratio, propeller reduction gear, impeller gear ratios or the substitution of major engine parts which requires extensive rework and testing of the engine.
  • Changes to the engine by replacing aircraft engine structural parts with parts not provided by the manufacturer.
  • Installation of structural parts other than the type of parts approved for the installation.
  • Changes to specifications or grade of fuel so that they differ from those listed in the engine specifications.
Propeller Major Modifications

Modifications to propellers listed below, when not listed in CAAC approved aircraft technical data, propeller major modifications.

  • Changes in blade design.
  • Changes in hub design.
  • Changes in the governor or control design.
  • Installation of a propeller governor or feathering system.
  • Installation of propeller de-icing system.
  • Installation of parts not approved for the propeller.
Airborne Equipment Major Modifications

Alterations of the basic design not made in accordance with recommendations of the appliance manufacturer or in accordance with a CAAC Airworthiness Directive are appliance major alterations.

Additionally, changes in the basic design of radio communication and navigation equipment approved under type certification or a Technical Standard Order (TSO) that have an effect on frequency stability, noise level, sensitivity, selectivity, distortion, spurious radiation, AVC characteristics, or ability to meet environmental test conditions and other changes that have an effect on the performance of the equipment are also major modifications.

In Part 2 of this post we will outline the MDA application and approval process.

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