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MD500/520 REPLACEMENT
HYDRAULIC CARGO HOOK KIT

Onboard Systems has developed a new hydraulic cargo hook kit for the MD500/520 helicopters, which was recently certified by the FAA and will begin production shortly. Onboard is also planning to submit the kit to Transport Canada so that it can be certified for use in Canada.

The legacy hook installed on the MD500 has a history of inadvertent cargo releases, which have been traced back to improper rigging and routing of the manual release cable on this aircraft. If the rigging isn’t set up properly, there may not be enough slack to allow for normal movement of the hook during external load operations, which could cause the hook to open unexpectedly. Our new kit features a hydraulic release cable that doesn’t require any rigging adjustments at installation, and offers a simplified route along the aircraft belly.

Eliminates the common causes for inadvertent releases

Recently, Onboard Systems has pioneered and developed hydraulic technology to serve as the emergency release for a number of critical reasons. The United States Department of the Interior Aviation Management released a Technical Bulletin dated July 16, 2004 that outlined common safety issues involved in inadvertent cargo hook releases. Their major findings were:

  • Cables must be rigged to very exact specifications each time the hook is installed on the aircraft
  • Cables are prone to damage that can cause a load release

The Onboard hydraulic release mechanism consists of a small, self-contained hydraulic reservoir that is used to open the hook. It does not use any hydraulic power from the aircraft. The hydraulic release is activated with a cabin-mounted lever that incorporates a compact master cylinder. A slave cylinder integrated in the cargo hook interfaces with the release mechanism.

Excessive movement during external load operations can unintentionally activate an improperly rigged manual release cable on a cargo hook system, causing an inadvertent release of the load. The hydraulic system presents a significant safety advantage because if the hydraulic cable gets snagged or damaged, it will not result in an accidental release of the cargo.

System Advantages

The hydraulic release offers significant advantages for installation, maintenance and operation:

  • Installation — Manual "push-pull" cable release systems need to be installed with very precise limits in order to make sure the system performs properly. A mistake one way could prevent the system from opening the hook; a mistake the other way could lead to the system accidentally opening. The nature of the cabled systems requires very large radius bends. The hydraulic system is not subject to any of the tight rigging requirements and can be installed with very tight bends, offering greater flexibility in routing the cable from the hook to the flight controls.
  • Maintenance — For similar reasons maintenance is simpler with a hydraulic system. A dry-break, quick-disconnect allows the hook system to be removed without any hydraulic fluid loss or need to bleed the complete system. And because our hydraulic cable is made of braided stainless steel and is very durable, this product will be very cost-effective and easy to maintain over time.
  • Operation — If a mechanical cable gets snagged or hit by the load it can inadvertently open the hook causing the loss of the cargo. The hydraulic system will only open the hook when the pilot activates the release handle — snagging or damage to the cable will not lead to accidentally dropping the cargo.

For more information, please visit our MD500 Cargo Hook product page.