The U.S. Federal Aviation Administration has grounded 2,715 Bell helicopters to order immediate inspections for improperly installed control bearings. The FAA terms this a, "critical unsafe condition" in requiring the short compliance time.

Affected models are the Bell 206A, 206B, 206L, 407 and 427 models.

Before the next flight, the FAA requires inspecting each cyclic control lever assembly that has less than 50 hours in service. The inspection is to determine if the bearing may be improperly installed or improperly staked in the lever assembly.

The Airworthiness Directive was the result of a report of an recently installed, but incorrectly installed bearing in the co-pilot's cyclonic control lever assembly. Improperly assembled, the bearing can fail, causing loss of control of the helicopter.

The Bell Alert Service Bulletins are 206-09-121, 206L-09-155, 407-09-85, and 427-09-23, dated March 10, 2009.

Bell's service bulletins indicate the company became aware of two instances where the bearing migrated out of the flight control lever because it had not been staked during assembly. Most troubling, each individual piece had been marked as fully inspected by Bell's supplier.

In a related understatement, Bell said: "Review of the supplier’s manufacturing and quality process indicates inspection of additional components is warranted."

In other words, Bell has decided to be cautious and has issued a second series of Service Bulletins, requiring that every bearing component -- six, in all -- from that particular vendor be inspected to ensure that the bearings are installed properly.


Bell Helicopter Alert Service Bulletin 427-09-25 for the 427 series (others similar)

Bell did not indicate why every bearing -- presumably from different manufacturing processes or cells -- should be inspected. It is possible, but not likely, that a vendor would use the same bearing staking machine for every different component produced.

A Bell spokesman said the company itself discovered the improperly installed bearings in the co-pilot cyclic controls. It was reported when Bell's Canadian arm set out to deliver a new helicopter. The situation was immediately reported to the Canadian aircraft authorities, Transport Canada.

Failed or displaced bearings in the co-pilot cyclic controls can lead to control malfunction and crash.

Although authorities have ordered inspections of all the potentially affected helicopters, Bell said it hopes visual inspections will reduce the number of affected helicopters to around 110. So far, it has not found any others in the in-service fleet.

Affected helicopters are not only in civil aviation, emergency and commercial use, but also in military deployments around the world.

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