This article, first published in July 2014, has been updated in April 2026.

An A321 flight crew reported hearing loud noises coming from the cargo hold during the approach and landing phases.

Once on the ground, inspection of the forward cargo hold revealed no damage to the cargo linings, but all container restraining XZ latches were lowered.

Investigation concluded that the XZ latches were not correctly locked before takeoff. The container that was loaded in the cargo hold was therefore not locked in position. It moved during the approach and landing phase, causing the noise that was heard by the flight crew.

The standard A320 family cargo hold is configured for bulk loading only, however, around 20 percent of the fleet is equipped with the optional semi-automatic Cargo Loading System (CLS).

The CLS is an electrically powered system that moves the ULDs in the aircraft cargo hold. The main goal is to reduce manpower and loading/unloading time.

The CLS is composed of several components, which can be grouped according to their intended functions (fig.1):

• Guidance, thanks to entrance guides on each side of the cargo entrance, and YZ guides located along each side of the cargo holds.
• Transport and Conveyance, performed by Power Drive Units (PDU) that push ULDs on the ball mat area and on the roller tracks.
• Restraint of ULDs, ensured by XZ latches, installed on the centre roller track.

(fig.1) A320 Family CLS components

The ULDs are maintained in position by XZ latches, which consist of an aluminium frame and a pair of spring-loaded interlocking pawls.

If the outside pawl is lifted up, the inside pawl extends and locks automatically. Conversely, if the inside pawl is depressed into the retracted position, the outside pawl automatically folds down (fig.2).

(fig.2) XZ latch 2842T100 series

Once each ULD is in position, the loading procedures call for these XZ latches to be raised and locked manually (fig.3).

(fig.3) XZ latch manual operation

Each ULD is then restrained by one XZ latch on each side of their baseplate or by one latch and one end-stop for those located at the borders of each holds (fig.4).

(fig.4) A321 FWD cargo hold, ULD, XZ latches and End stops positions

ULD movements are rare occurrences on A330, A310, A330, A340, A350 and A380 aircraft, because most loading configurations call for 2 latches on each side of the ULD baseplates. Moreover, the wide body aircraft often fly with fully loaded cargo holds.

Several causes of unwanted ULD movement have been identified based on the events reported by operators.

If the loader does not raise up the latch or does not properly lock it into position, the container / pallet will not be restrained in the X (flight) direction and will therefore move freely.

Prevention means:

• Awareness

The Weight and Balance Manual (WBM, chapters CTL-LIM) and Aircraft Maintenance Manual (AMM, chapter 25-52) specify that loaders must raise and properly lock all latches, regardless of whether the positions are empty or not.

• Design improvement

If the outside pawl is lifted up, the inside pawl extends and locks auto­matically.

A weak spring may not extend the inner pawl enough when the outside pawl is lifted up, leaving the latch in an intermediate (unlocked) position. The design improvement calls for an increased spring force.

This design equally calls for the addition of an easily visible yellow indicator when the latch is in an intermediate position, i.e. not raised enough to be in the locked position (fig.5 and 6).

This latch (Part Number 2842T100-3) has been introduced in production from MSN 0573 onwards (Feb 1996) and is proposed through the Illustrated Parts Catalogue (IPC) as an alternative.

(fig.5) Latch correctly locked: the yellow indicator
is not visible

(fig.6)  Latch in intermediate position, not correctly locked: the yellow indicator is visible

An inoperative or damaged latch may as well lead to ULD movements.

Prevention means:

The following A320 Family Maintenance Planning Document (MPD) tasks call for visual and operational checks of the XZ Latches:

• Task 255000-11: “Visual check of the XZ latches and door sill latches” Interval: 12 months or 1000 FH.
• Task 255000-02:”Perform Operational Check and Detailed Inspection of XZ-Latches ” Interval: 72 months or 8000 FH.

A third task requests a detailed inspection of the latch after removal. The removal of the part allows for an easier inspection, especially regarding the spring condition.

• Task 255000-25: “Remove XZ latches for detailed inspection” Interval 180 month or 24000 FH. 

Damaged, deformed, or non-standard ULD baseplates may also impair the proper functioning of the latch.

Prevention means:

ULDs should comply with National Aerospace Standards (NAS) 3610 and IATA specifications during their entire lifetime.
ULDs should be loaded in accordance with the WBM.
Airbus highly encourages airlines to clean their cargo hold to avoid debris that could interfere between the ULD baseplate and the XZ latch, as recommended in Task 12-21-12-100-007-A ”Cleaning of the Cargo-Compartment Floor Areas”.

This scenario is excluded when the cargo is fully loaded. In such a case, both pawls of every XZ latch are blocked by the adjacent ULD baseplate.

(fig.7) Recommended A321 AFT cargo hold loading sequence

(fig.8) Latches in locked position after loading

Airbus encourages operators to communicate any suspected or confirmed case of ULD movement by means of a specifically designed reporting sheet, available in ISI 25.50.00004 and has been specifically produced to facilitate the search for the root cause of the movement.