McDonnell Douglas Helicopter Systems (MDHS) Explorer helicopters have been grounded "until further notice" following the discovery of a broken adjustable collective drive-link. Subsequent tests have revealed the need for a redesign of the assembly.

The company notified operators of the grounding order on the evening of 28 May, saying that the grounding "-could last something less than a month". As Flight International closed for press, MDHS engineers were in emergency session to "-discuss alternatives", says the company. "These range from something as simple as inspections every X hours to the complete redesign and rebuilding of the piece."

MDHS says that the design and manufacturing of a new assembly is "not a significant issue", but admits that the swift retrofit of the current fleet will be a major exercise.

The problem cropped up on 8 May when a US operator discovered a broken adjustable collective drive-link, part of the rotor-head system, during a post-flight inspection. At this stage, it is not known if the failure occurred in flight or on the ground. "If the aircraft had been inflight when it happened, then a second connection would have done its job and the flight would have continued safely, but the connection that broke is a 'no-go' item," says MDHS. The second, dual path, fixed-link assembly continued to function in the 8 May incident and is not affected by this action, the company adds.

MDHS on 9 May advised operators of the incident and began shipping replacement link assemblies. Subsequent laboratory tests have revealed fundamental flaws in the design, however, which can only be cured by a major redesign. "Time required to design, test, manufacture and distribute new link assemblies is not known," the company says.

Source: Flight International