A A319 aircraft was performing a non-revenue flight from its main base, following a maintenance check. There were two passengers and two flight crew members onboard. During climb, a CAB PR EXCESS CAB ALT ECAM warning triggered. The flight crew initiated an emergency descent and opted to perform an in-flight turn back. The aircraft safely landed without further incident.

During troubleshooting, the maintenance crew observed that the aft cargo door pressure seal was incorrectly installed.

Records showed that the cargo door seals were replaced during the maintenance check as per the mandatory Service Bulletin (SB) A320-52-1195.

The seal of the aft cargo door failed to inflate due to its incorrect installation causing an air leak, which caused the CAB PR EXCESS CAB ALT ECAM warning to trigger.

The aircraft safely returned to operation when the aft cargo door seal was reinstalled correctly and inspected.

Cargo door seals are made of reinforced silicone rubber and are installed in the retainer around the door structure. They ensure air tightness around the cargo door to maintain aircraft pressurization.

On Airbus aircraft, the airtightness of the cargo doors are ensured by inflatable seals. Inflatable cargo door seals have inflation holes located on their inner surface (the cargo facing side) of the seal, that allows the pressurized air from the cabin to enter the seal, which causes it to inflate as the altitude increases and this ensures the airtightness around the seal (fig.1).

(fig.1) Concept of an inflatable seal - typical view

If the inflatable seal is installed incorrectly, and the inflation hole is in the wrong position, the pressurized air can compress the seal and create air leaks (fig.2).

(fig.2) Incorrect installation of the inflatable seal can create air leaks

Two potential effects from incorrect seal installation include pressurization issues and the reduced effectiveness of the cargo fire extinguishing system. Air leaking around the cargo door seal can make it difficult to pressurize the aircraft, or it can potentially cause an in-flight depressurization event requiring an emergency descent. In the event of a cargo fire, the air leaking around the seal may allow the extinguishing agent to escape the cargo compartment and fail to extinguish the fire.

Most of the reported cases of incorrect seal installation occurred on A320 family aircraft for two main reasons:

The Airworthiness Directive (AD) 2021-0049 published by the EASA in March 2021 mandates the installation of a new seal via Service Bulletins (SB) before March 2029 on all in-service A320 family aircraft delivered before November 2019. SB A320 52-1195 (for CEO aircraft) and SB A320 52-1196 (for NEO aircraft) require replacement of the aircraft’s cargo doors seals, canceling the need for repetitive cleaning and greasing of the old seal requested by the AD pending its replacement. The new seal has improved airtightness and does not require regular greasing to improve its efficiency.

This mandatory replacement of the seals on A320 family aircraft significantly increases the risk exposure to incorrect installation of the seal. Replacement of a cargo door seal is normally only performed when it is damaged during operation.

Another reason A320 family cargo doors may have reported incorrect installations is because the seals on A320 family aircraft have a symmetrical shape and they are more flexible when compared to the seals installed on other Airbus aircraft models. On the other aircraft types (A220, A300, A310, A330, A340, A350 and A380 aircraft), the seals have a higher rigidity and some have an asymmetrical shape, which can aid the operator to correctly install the seal.

Even if A300, A310, A330, A340, A350, A380 and A220 aircraft are less prone to incorrect installation, maintenance personnel must carefully follow the AMM/MP/AMP instruction to ensure that the seals are installed correctly. This includes careful consideration of the warnings, cautions, procedure and illustrations.

A recommendation as an additional safety barrier is to require an additional inspection and dual signature for the cargo door seal installation task.

To prevent incorrect seal installation, the seal manufacturer has introduced an instruction notice included with seal deliveries (fig.3). This notice highlights the need to pay particular attention to the correct orientation of the cargo door seal holes.

Maintenance personnel must ensure that the inflation holes are located on the inner side (the cargo facing side) of the door. In addition, the cargo door seals do not have inflation holes in their lower part and so the maintenance personnel must ensure that the side of the seal marked with “LOWER DOOR” is positioned closest to the door locking mechanism (fig.4).

Maintenance personnel should install the four pre-formed corners first to ensure the seal is in the correct position and to prevent wrinkles. White alignment marks help to identify and correctly position the pre-formed corners (fig.5).

(fig.5) Installation of the pre-formed corners before the straight sides ensures correct installation of the seal along the door frame

A careful inspection of the seal as per AMM is required to ensure correct seal installation. The maintenance personnel must inspect the entire circumference of the cargo door seal. They must ensure the seal is not twisted and check that the inflation holes are facing towards the inner side of the cargo door by gently bending the seal (fig.6).

Airbus developed an awareness video to illustrate these essential steps for correct cargo doors seal installation on the A320 family.