AD Compliance

The Barbed latching system (secondary latching) is a significant enhancement in flight safety and was developed in light of a requirement by the CAA to find a solution to the problem of cowlings detaching in flight on the Eurocopter AS350 and AS355 Series Aircraft.

This latching system is approved for installation on the Eurocopter AS350 and AS355 series aircraft under Aerospace Design Facilities Ltd modification number ADF 350/5-101 and was approved by the UK CAA under minor mod approval number 9/214/M/4126. The CAA have published two Airworthiness Directives 002-10-2001 & 003-10-2001 which, originally only include the barbed latching system by name as an acceptable form of compliance this is because it was the only currently approved modification at the time of issue.

The modification covers the installation of one barbed latch to each applicable engine or gearbox cowling on the AS350 series, AS355F series and the AS355N series. This latching system is supplied in kit form ready for installation with full aircraft release from an approved manufacturer .

 

The principal of this latch is identical to the secondary bonnet latch installed on every modern car today. It holds the bonnet in the ‘nearly closed’ position if the primary latch has not been secured properly. Although this latch system for the aerospace industry is fundamentally different to cope with the flexibility of modern composite cowlings and has redundancy features to give a continued latching function under primary failure modes.

This latching system is a good human factors approach to the current problem. When the cowling is lowered from any point in its range of travel to its nearly closed or rest position, the cowling is retained with the airframe without any further human intervention. It also ensures that the cowling is retained irrespective of the primary latch position.

The integrity of the latch system being a stand-alone solution does not rely on the current modification status of the aircraft to which it is installed. The only criteria applied to any existing modification state is that the cowling is ensured an unrestricted "free fall" path to the relaxed position where the cowling comes to rest against the airframe.

The secondary latch system by design incorporates a redundancy feature that ensures that the latch will still retain the cowling under certain failure modes. This is ensured by the fact that the latch cannot be released from the mating part without both fingers being retracted simultaneously and that both fingers are individually sprung biased in an outward direction.

The modular construction of the latch can be easily maintained by the nominated maintenance organisation. If a fault is detected with any unit it can be changed with a serviceable unit very quickly ensuring that the operator experiences the minimum of inconvenience.

It is a robust latch, which retains the cowling with the airframe when all other visual indications may have been missed. The installation of any of these secondary latch kits only involves minimal local disturbance at the latch attachment points.

Irrespective of the aircraft type each kit involves the installation of one latch to each affected cowling and its receptacle on the mating part of the airframe. All latches installed are identical across all AS350 and AS355 types and are therefore easily interchangeable.

Once the latch has engaged the cowling with the airframe it can only be released by a push button accessible on the outside of the cowling. The secondary latching system addresses the retention of the cowling with the airframe instead of trying to make it more visually obvious that the panel is not properly secured in the first place, which has been the method so commonly used in the past.

 

If (on a cowling without secondary latching) all the visual indications are missed for an improperly latched cowling, the inevitable consequences of that cowling rising into the airflow and separating from the airframe can not only be costly but also catastrophic.

Each kit variant contains full detailed installation instructions for each aircraft cowling of the relevant aircraft type. Aerospace Design Facilities Ltd feels that the secondary latching system is a good simple, mechanical and practical solution to the problem of unsecured cowlings. It is a physical mass that can be easily inspected and assessed prior to each flight for its integrity and serviceability. It retains the cowling with the airframe in the event that the latches are left unsecured.

All installation kits are supplied with full release paperwork, drawing packages and installation instructions.

 

For current price and availability please contact us with the relevant kit part number listed below:

 

Eurocopter AS355F kit Pt no. ADF 350-101-100-01 -installed under mod no.ADF 350/5-101 - PART F
Eurocopter AS355N kit Pt no. ADF 350-101-200-01 -installed under mod no.ADF 350/5-101 - PART N

Eurocopter AS350 kit Pt no. ADF 350-101-300-01 -installed under mod no.ADF 350/5-101 - PART B