The FAA issued an emergency Airworthiness Directive last month to all Robinson R22 owners and operators, calling for them to carry out immediate checks to assess the serviceability of their main rotor blades.
The bulletin was prompted by two accidents–in Australia and Israel–that were
attributed to blade failure. Post-accident investigation revealed that corrosion from water penetration had initiated fatigue cracks in the blades. It was established that the cracked blades manifested themselves, initially, in an increase in helicopter vibration. Following a track-and-balance of the blades, the vibrations would go back to normal for a short time and then slowly increase again, until blade failure occurred. If not prevented, the condition could lead to a fatigue crack, followed by blade failure and subsequent loss of control.
Within 10 flight hours or 30 days, owners of all R22s are advised to establish the age of their blades and carry out an immediate rotor track-and-balance on any that are five years old or have 1,000 hours in-service. If any abnormal increase in vibration occurs within five hours of the last track-and-balance, the operator should replace the blades immediately. Older A016-1 blades should be replaced in any case before reaching 2,000 hours, or in the case of A016-2 blades before 2,200 hours.
This AD also revises the limitations section of the maintenance manual by adding a new retirement life of 10 years to the current 2,200 hours in-service life. The blades must be retired upon reaching 2,200 hours or 10 years, whichever occurs first.
AD 2004-06-52, dated March 18, can be found online at www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf by clicking on “emergency ADs.”