Dozens of New Zealand aircraft were effectively grounded after a fault was found in their emergency locator transmitters.
The units have an automatic switch - the G-switch - that turns the transmitter on when the aircraft crashes.
The fault stopped the switch from working.
The problem affected some Artex brand transmitters supplied by United States company Cobham Avionics Artex Products.
The Civil Aviation Authority (CAA) estimated there were more than 1300 in New Zealand aircraft, and 200,000 worldwide.
Locator transmitters are compulsory in New Zealand and aircraft usually cannot be flown without them, except to be flown to where they can be fixed.
CAA spokesman Bill Sommer has confirmed at least 90 faults were discovered in the two years to April, and another 30 were found from late June.
Mr Sommer said New Zealand was the first to report the fault and the CAA was working with Artex and the United States Federal Aviation Administration to get it resolved.
A CAA report in January said Artex-manufactured systems had an unacceptably high G-switch failure rate.
All 26 reported failures between July 2008 and November 2009 were for Artex switches.
Even so, the failure was now not a "major issue" as it had been identified and appropriate steps had been taken to minimise the risk, Mr Sommer said.
The CAA issued an Airworthiness Directive requiring transmitters to be checked every two months rather than every two years, and Artex was tackling a shortage of replacement switches to meet demand.
The transmitter could be started manually using a control inside the cockpit and the authority reinforced its longstanding advice for pilots to turn it on when they got into trouble, Mr Sommer said.
"The G-switch is supposed to operate after rapid deceleration but we are advising people that it is much better not to wait for the bang."
Aircraft Owners and Pilots Association president Hamish Ross said he believed Artex had at least half of New Zealand's emergency locator transmitter market, and that most would have been installed when they were made compulsory in July 2008.
It was sobering to think some of the fail-safe switches might have had a fault but the focus was now on the "nuisance" of more regular testing while alternatives were designed.
Lower South Island representative Murray Paterson, of East Taieri, said many of the association's members used another system but hoped more regular testing would keep on top of the fault.
Palmerston North company Feildair, which repairs the switches, confirmed it fixed about 180 in the past two years and about 60 in the past three months.
Instruments and avionics engineer Chris McLaughlin said that stretched spare-part supplies but that the rate should slow now that all transmitters had been tested at least once.
Taieri Airport-based Southair engineer David Patrick said he had dealt with a couple of failures, and that he hoped a new switch could be developed to replace the "old replacements".
Cobham Avionics Artex Products' Arizona offices were closed and company representatives could not be contacted.
