OPERATIONS
Correct Cargo Door Seal Installation for Safe Operation
Incorrect installation of a cargo doors seal may lead to unsafe in-flight operations such as abnormal cabin pressurization or an ineffective cargo fire extinguishing system.
This article recalls the essential steps of the AMM for correct cargo door seal installation, including the required inspection after installation.
CASE STUDY
Event Description
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.
Event Analysis
Cargo door seal found incorrectly installed
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 SEAL
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.
Seal Design
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
Incorrect Installation Causing Air Leaks
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
Effects of incorrect installation
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.
Increased Risk Exposure on A320 Family Aircraft
Most of the reported cases of incorrect seal installation occurred on A320 family aircraft for two main reasons:
High number of cargo door seal replacements required by service bulletin
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.
Different seal characteristics
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.
ENSURING CORRECT CARGO DOOR SEAL INSTALLATION
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.
Additional inspection and dual signature
A recommendation as an additional safety barrier is to require an additional inspection and dual signature for the cargo door seal installation task.
Ensuring correct seal installation on A320 family
Introduction of a caution tag
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.
(fig.3) Instruction notice included with seal deliveries
Correct positioning of the seal
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).
(fig.4) Example of Correct positioning of an aft cargo door seal on an A320 family aircraft
Installation of pre-formed corners
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
Mandatory Visual inspection
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).
(fig.6) Slightly bending the seal enables the maintenance personnel to check the inflation holes are facing towards the inner surface of the door, which is the cargo side
A320 Cargo Doors Seal Installation Video
Airbus developed an awareness video to illustrate these essential steps for correct cargo doors seal installation on the A320 family.
Video: A320 Family – Cargo door seal installation
Further information can be found in the AMM/AMP and on the AirbusWorld portal and in the following documents:
- OIT Ref.: 999.0040/23 – ATA 52 – CARGO DOORS SEALS INSTALLATION
- ISI Ref.: 00.00.00437 – A320 Family Systems Ageing global ISI
- Maintenance Briefing Notes (MBN): Forward & aft cargo door seal installation
- TFU Ref.: 52.30.00034 – A320 Fam CARGO COMPARTMENT DOORS SEAL ADAPTATION FOR HALON LEAKAGE IMPROVEMENT
- RIL Reference: SA52M20001620
On Airbus aircraft, the airtightness around the cargo doors is ensured by an inflatable cargo door seal. The inflation holes must be correctly oriented towards the inner surface of the door, which is facing the cargo, to function correctly. Incorrect installation of the seal may lead to a failure to pressurize the aircraft, loss of aircraft cabin pressure inflight, or cause the cargo fire extinguishing system to be less effective in the event of a cargo fire.
The AMM/MP/AMP provides instructions, warnings and illustrations to ensure correct installation of the cargo door seal and reminders are now also attached to each replacement seal for A320 family aircraft.
Once the seal is installed, a visual inspection of the entire seal is required to ensure that the seal is not twisted and the inflation holes are oriented towards the inner side of the cargo doors. It is recommended to require an additional inspection and dual certification of a cargo door seal installation task as an additional safety barrier.
Contributors
Markus ADLER
Metallic Structure Design Responsible
Design Office
Christophe DELMAS
Aircraft Safety Enhancement Manager Specialist
Design Office
Jean Philippe JACQ
Safety & Maintenance Expert
Customer Support
Cyril MONTOYA
Product Safety Enhancement Manager
Customer Support
With Thanks to Cesar GARCIA CASTILLA Product Safety Enhancement, Damien PARISE Customer Support Structure Fuselage Engineer