Modifying & repairing aircraft

One of the main features of the LAA system is that modifications and repairs can be approved with significantly reduced costs compared with aircraft on Certificates of Airworthiness, where applicants would need to deal with the CAA or EASA. Since the engineering team are all ‘little aircraft’ experts, it is usually a straight-forward job to approve many types of change.  Of course, with many of our members being so creative, sometimes the job takes a little more time and thought to approve!



There are five levels of modification:




Further Details

Apply Using


Application Fee


The Prototype (“normal”) modification

This is a normal modification application made in the usual way and is applicable only to the aircraft for which the application is made.

Technical Leaflet

TL 3.01

LAA/MOD 2 and


* see below


The Repeat modification

This is a modification that has already been approved on one aircraft as a Prototype modification, but is now requested by the owner of a subsequent aircraft to be applied to their aircraft.  The detail of information available may not be as much as for a Standard modification. Note that a Repeat modification must identically replicate the original Prototype modification including fasteners and positions of parts and should generally be on the same aircraft type as the original.

Technical Leaflet TL 3.07


List of Prototype mods since 1/1/08 (TL 3.17)


* see below


The Standard modification

This is a modification that is very well defined and is applicable to a particular aircraft or engine type or types.  Members may continue to nominate new Standard modifications using form LAA/MOD 9; however, LAA Engineering may choose to convert popular Repeat modifications into Standard modifications.

Technical Leaflet TL 3.06


See list and details of approved Standard modifications



Also see individual modifications for details

Variable, see individual modifications for details


Manufacturers’ modifications

Kit manufacturers and plans suppliers often have long lists of optional modifications that can be fitted and during the lifetime of a type product improvements are introduced.  Generally, LAA-accepted optional items are listed on the TADS for the type. 

Not applicable

Not applicable

Not applicable

5 The Trivial change Sometimes a change is so trivial that no application is required and there is no need to inform the Engineering department. Technical Leaflet TL 3.10 Not applicable Not applicable
6 STCs Where a change has previously been approved by means of a Supplemental Type Certificate (STC), LAA Engineering then only needs to investigate any installatin/compatibility issues rather than the change itself. Not applicable LAA/MOD 13 £30



Avionics installations

These are not considered modifications, but in order to fulfil their legal obligations, owners are required to keep LAA up-to-date should radio details alter.  A special system exists for the approval of radio changes that is separate from other modifications.  The procedures in TL 3.03 must be followed.

Technical Leaflet TL 3.03


No charge for radio/transponder installations, but a £30 fee is chargeable for certified ADS-B Out applications - see TL 3.03


Engine and propeller changes

These are treated as Prototype or Repeat modifications as per the above definitions, unless they appear on the PTL list for the type.

Technical Leaflet TL 3.02


PTL/1 Lists




* see below


Category changes

Applications to change an aircraft’s category from a microlight to a ‘Group A’ aircraft (and vice versa) are allocated a modification number to record the change.  If an engine or propeller change is required at the same time, then an application must be made as noted above.





* All prototype modifications (including engine and propeller changes) attract a minimum fee of £60 which covers up to two hours' work; all repeat modifications (including engine and propeller changes) attract a minimum fee of £30 which covers up to one hour's work. Thereafter, work is charged at £30/hour in either case. See the relevant Technical Leaflet for the type of modification for further details.



 A repair is defined as:


“A deviation from the approved design which arises unintentionally either during manufacture or in service”


Further information on repairs can be found in Technical Leaflets TL 3.05 and TL 3.13 (composite repairs).  Applications for repairs are to be made on form LAA/MOD 8.  Charges are made in the same way as modifications, above (£60 minimum fee, £30/hr).


Note that ‘repairs’ made by replacing a whole part with a new, authentic spare part (e.g. replacing a damaged landing gear member with a new one from the importer) does not need an application and can simply be signed off by an inspector in the logbook.