AAIB investigation to Aero L-159E, G-DKNA

Rapid descent due to failure of main and emergency aircraft oxygen systems, North Sea Danger Area (D323 D), 27 October 2025

• From: Air Accidents Investigation Branch
• Published: 12 November 2026

• Category: General aviation - fixed wing
• Report type: Bulletin - Correspondence investigation
• Date of occurrence: 27 October 2025
• Aircraft type: Aero L-159E
• Location: North Sea Danger Area (D323 D)
• Registration: G-DKNA

During a high-altitude sortie at night, a cracked inlet air supply pipe led to the failure of the aircraft’s main oxygen system. This was compounded by a failure of the emergency oxygen system, due to a latent fault within the oxygen regulator. This resulted in the pilot being briefly exposed to a risk of hypoxia and required an emergency descent of the aircraft through controlled airspace. As a result of its internal investigation, the operator is considering a number of safety actions to address the issues identified with the aircraft oxygen supply system and its maintenance and testing.

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Aero L-159E, G-DKNA 11-26

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