Perkoz SZD-54-2: from crack inspections to a modified assembly

The new EASA directive on the SZD-54-2 Perkoz is more than an update to inspection requirements. Its significance lies above all in the identification of the cause of the cracks and the development of a modified airbrake control assembly.

In my view, AD 2026-0199 is best read as the continuation of a single technical problem: from the first inspections, through identification of the cause, to a change in the design.

Which part cracks and what it does

The problem does not concern the airbrake surfaces themselves. The damage occurs at the welded joint between the control lever and the torque tube of the airbrake drive mechanism, located in the fuselage. The lever and the torque tube form the link through which control movement is transmitted to the airbrake drive.

Crack growth in the area of the welded joint can reduce the mechanism's ability to carry loads and lead to loss of airbrake function. The result may be reduced airbrake effectiveness and, in the extreme case, its complete loss. Loss of airbrake effectiveness matters most during the approach to landing, when the airbrakes are used to control the glide angle and manage the glider's energy.

From AD 2026-0086 to AD 2026-0199

EASA issued AD 2026-0086 in April 2026 (issued 30 April 2026, effective 7 May 2026). At that time the cause of the observed cracks had not been clearly established. The directive was based on Allstar PZL Glider bulletin BE-004/54-2/2026 of February 2026 and served to detect damage.

Further analyses and calculations confirmed the fatigue nature of the cracks, and the manufacturer developed a modified assembly. This is reflected in AD 2026-0199 (issued 20 October 2026, effective 3 November 2026). The directive refers to Allstar PZL bulletin BE-004/54-2/2026 at Revision 1 of 22 June 2026. The first document therefore served to detect damage, while the second also points to a design solution.

What the fatigue nature of the cracks means

Material fatigue means that repeated loads can initiate and propagate cracks even when a single load is far below the material's strength limit. In welded structures, stress concentration points such as joints tend to be particularly sensitive. This is a general principle, not a finding specific to the Perkoz.

With regard to this particular assembly, the directive confirms the fatigue nature of the damage without presenting a detailed analysis of where the cracks initiate.

Repetitive inspections make it possible to detect developing cracks, but they do not eliminate the fatigue mechanism responsible for them.

How the damage is detected: three types of inspection

The directive provides for GVI and DET inspections, and an SDI inspection carried out in specified cases. GVI is a general visual inspection, DET is a detailed inspection, and SDI (Special Detailed Inspection) is a special detailed inspection carried out in accordance with a defined procedure.

The stated intervals are the maximum permitted intervals. GVI is carried out at the latest every 200 flights. The 10-flight tolerance is not cumulative. It may be used only to synchronise the GVI with other maintenance tasks for which the maintenance manual already provides a corresponding tolerance. It is not a standard extension of the interval to 210 flights. DET is carried out at the latest every 300 flight hours or 12 months, whichever occurs first.

The SDI inspection is carried out in the cases provided for in the bulletin, and is mandatory before the next flight if signs of a crack were found during a GVI or DET or if its presence cannot be ruled out.

The inspection method and the assessment criteria are set out in bulletin BE-004/54-2/2026 Revision 1 of 22 June 2026, available in the SZD-54-2 Perkoz technical documentation on the manufacturer's official website.

The repetitive inspections apply to gliders up to and including serial number 542.A.25.049. AD 2026-0199 itself, however, covers all SZD-54-2 serial numbers, so the scope of the inspections should not be read as the scope of the whole directive.

The initial deadlines follow from the effective date of AD 2026-0086, that is 7 May 2026. A GVI was required before the first flight after that date. A DET had to be carried out within 300 flight hours or 12 months from 7 May 2026, whichever occurred first. After that, the repetitive intervals given above apply.

New assembly, replacement and installation restrictions

The existing assembly is P/N 540.64.30.00 and the modified one is P/N 542.64.30.00A. The directive identifies the modified assembly as the solution to the fatigue problem but does not present details of its design.

EASA does not require immediate replacement of all older assemblies. Replacement with P/N 542.64.30.00A is required when the inspections mandated by the AD reveal the discrepancies specified in the bulletin. It must be carried out in accordance with the manufacturer's instructions before the next flight.

Replacement with the modified assembly P/N 542.64.30.00A, carried out in accordance with the manufacturer's bulletin, is the terminating action for the repetitive GVI and DET inspections specified in paragraphs (1) and (2) of AD 2026-0199.

From 3 November 2026, installation of P/N 540.64.30.00 is prohibited. The exception is removal and reinstallation of the same part on the same glider during a single maintenance visit. Such reinstallation does not, however, exempt the operator from the remaining requirements of the AD, including the obligation to replace the assembly if discrepancies have been found.

What changed once the cause was established

The most important aspect of AD 2026-0199 is the availability of the modified assembly developed in response to the identified fatigue problem. The Perkoz case shows how establishing the cause of damage makes it possible to move from periodic detection of its effects to the implementation of a design solution.

About the author

Adrian Nafalski, MSc Eng.

Specialist in aircraft maintenance and continuing airworthiness management. Holder of an EASA Part-66 licence in categories B1.2, B1.4, B2 and C. He also works on avionics, the digitalisation of aviation processes and the use of artificial neural networks in technical diagnostics. Originator of the Aeronite environment.

Source: ad.easa.europa.eu/ad/2026-0199