Engineering Matters

Including: Undercarriage strut corrosion, clarification of ‘600kg microlight’ definition, plus advice to help HQ with a speedy Permit revalidation

Welcome to ‘Engineering Matters’ – the section of Light Aviation that is dedicated to discussing all manner of topics concerning both technical and operational aspects of the LAA fleet. If you have anything to say that you think would benefit others, then please email words and pictures to LAA Engineering at engineering@laa.uk.com

Piper Cub main landing gear strut corrosion

Piper J3C Cub owner, Philip Whiteman, has reported that he was shocked to find severe corrosion on one of his aircraft’s main undercarriage struts.

The aircraft was undergoing a thorough inspection after a period out of the air, and when inspecting the undercarriage and servicing the wheels and brakes, some serious corrosion on the underside of the port bungee strut was discovered.

Philip said that from the usual viewpoint when carrying out the pre-flight checks, the undercarriage looked fine. The starboard strut appears sound, but that one has also been taken off for inspection.

It is thought that the port undercarriage is original to the aircraft, which was built in 1944. The components were inspected and refinished in two-pack paint 1994/95 and there was no sign of corrosion when the struts were removed for bungee replacement in 2003. The aeroplane lives in a dry, well-ventilated hangar and has

LAA Inspector Ray Harper has highlighted an issue discovered recently on a Pioneer 300 during the Permit to Fly revalidation annual inspection. The brackets, which attach the over-centre side brace to the main spar box, are retained in place by set screws which have backed out allowing the bracket been in the family a long time, so its maintenance and inspection history is well known. to move away from the main spar. Although one would hope that this was a fairly simple problem to rectify, it required the wing to be removed to access the screws.

With undercarriages, being close to the ground, they can suffer from stone damage and other forms of surface finish erosion, mud accumulation when operating away from tarmac, as well as contamination from hydraulic braking systems. Add to that the possibility of struts corroding internally, and the chances of corrosion and other defects are pretty high.

Retractable undercarriage systems on light aircraft are inherently complicated affairs that require regular inspection, maintenance and lubrication. The operation of the system should be routinely checked with the aircraft up on jacks. Not only is this vital to ensure the system’s correct operation, but is also a good opportunity for owners to understand how the system functions (get someone to operate it while you watch from a safe distance), and have a chance to get familiar with any emergency lowering systems. Once an emergency system has been used, it’s wise to carry out a further two or three normal retractions and extensions, to ensure everything has been ‘reset’.

If it’s an electrically powered system, if at all possible, use ground power to save the aircraft’s battery, or charge the battery up afterwards.

LAA Engineering housekeeping

G-INFO/LAA PO Box redirecting service renewals The facility to use the LAA PO Box number address has been in place for over a year. If you are a user of this service, please remember to reapply (and pay) for another year via the LAA online shop.

For new applications, please read the notes – we require both an application form to be submitted as well as the money!

600kg ‘Microlights’ With the recent advent of the 600kg microlight definition, owners are reminded that the rules do not automatically apply to any existing aircraft: your aircraft will continue to be classified (either as a microlight or a fixed-wing landplane) as before and with the same maximum weight as shown on your aircraft’s Operating Limitations document.

For instance, if your microlight was originally approved at 450kg maximum weight, you cannot operate above this weight unless LAA Engineering has re-issued the Operating Limitations to show a higher weight.

The new rules were designed to apply to new types evaluated against an updated airworthiness code, although there is some scope for us to re-classify some aircraft of types that straddle the divide – in this case a mod application is needed for us to evaluate the request and update the aircraft’s documentation.

FWR-1 Permit to fly revalidation applications Thank you for bearing with us during the traditional peak season of Permit to Fly revalidations. For applications that have been accurately completed, we are still managing to turn them around within a few days of receipt.

Where applications raise queries, these take time for us to contact owners and applicants in order for us to resolve the issues before the Permit to Fly can be revalidated. Please do not forget to thoroughly check the form before sending it in – it is surprising to see just how many come in with sections left blank or the front page unsigned.

Just like with a car MOT, you can apply for a Permit to Fly revalidation up to a month before expiry and the check flight can be done before the inspection.

This means that with some planning (and cooperation from the weather) you can get the application to LAA Engineering with plenty

LAA Engineering charges

LAA Project Registration

Kit Built Aircraft £300

Plans Built Aircraft £50

Initial Permit issue

Up to 450kg £450

451-999kg £550

1,000kg and above £650

Permit Revalidation

(can now be paid online via LAA Shop)

Up to 450kg £170

451-999kg £220

1,000kg and above £260

Factory-built gyroplanes* (all weights) £275

*Gyros note: if the last Renewal wasn’t administered by the LAA, an extra fee of £125 applies

Modification application

Prototype modification minimum £60

Repeat modification minimum £30

Transfer

(from C of A to Permit or CAA Permit to LAA Permit) of time to resolve any queries that might arise. We are looking at ways to help spread the peak workload for us and to make things easier for all involved, but please note that we cannot (yet) accept scanned copies of the application form.

Other thoughts concerning Permit to Fly revalidations

Open Mods If a modification has been applied for, it speeds up Permit to Fly revalidation applications immensely, if owners and Inspectors remember to add a note on page three of the FWR-1, confirming the status of the mod. If this is not done, then we have to contact the owner and Inspector to check on the mod status.

The Permit to Fly cannot be revalidated once the aircraft has been modified (even if the mod is not complete) and it should not be flown either unless LAA Engineering has confirmed otherwise.

Up to 450kg

451 to 999kg and above

Four-seat aircraft

Aircraft Document Check

There continues to be a large number of errors recorded on the FWR-1 Aircraft Document Check.

In theory, this section should be completed by the Inspector, once the Operating Limitations document has been compared to the installed engine and propeller (and placards).

This physical check is to ensure that the engine and propeller are the same as specified in the aircraft’s Operating Limitations document (or, in the case of propellers, as listed on the PTL/1 list). This means that if all is in order, the recorded engine and propeller designations should be exactly the same as found on the Operating Limitations document.

Check Flight The take-off weight for the Permit to Fly revalidation check flight should be in excess of 90% of the MTWA for the aircraft, as this makes aircraft performance monitoring more meaningful.

Additionally, the centre of gravity at take-off should be within the limits stated in the aircraft’s Operating Limitations document and use the same datum as specified – and please include the units of measurement, not a percentage of MAC, unless that is what is used in the Operating Limitations document.

It is surprising just how many applications are received with a centre of gravity that is outside limits and the incorrect ‘forward of datum’ or ‘aft of datum’ stated. ■

Recent Alerts & AILs

Please note the Engineering section of the LAA website has the most current information.

LAA TSB: TSB-001-2022

Applicability: All Europa aircraft

Europa: Door latch system stop

CAA MPD: 2022-003

Manufacturer’s/agent’s type acceptance fee £2,000

Project registration royalty £50

Category change

Group A to microlight £150

Microlight to Group A

Change of G-Registration fee

Issue of Permit documents following G-Reg change £55

Replacement Documents

Lost, stolen etc (fee is per document)£20

PLEASE NOTE: When you’re submitting documents using an A4-sized envelope, a first-class stamp is insufficient postage.

LAA AIL: MOD/247/012

LAA Alert: LAA/AWA/21/08

Note: CAA MPD 2022-003 has now been corrected as of 22 June 2022

MT-PROPELLER ENTWICKLUNG GmbH

Applicability: MTV-( ) Variable Pitch Propellers

Subject: Propeller Blade Lag Screw Replacement

EASA AD 2022-0134

Note: Please see the MT Propeller TADS P17 link to the ‘EASA AD Safety Publishing Tool’ for further info.

SLING

Applicability: All Sling aircraft types and serials

Subject: Eyebolt inspection and conditional replacement Sling Service Bulletin #0020

Note: It has been found that the eyebolts fitted in the control system of certain Sling aircraft may fail to meet the manufacturer’s specification in regard to fatigue life. Such eyebolts are identifiable by the narrowness of the neck of the eyebolt above the bolt thread. This service bulletin details the procedures for inspection and replacement of such eyebolts in the various control systems.