Nigerian investigators have isolated a batch of self-locking nuts for analysis after a nose wheel was lost during takeoff on a Green Africa Airways ATR 72-600.
The aircraft was en route from Ilorin in western Nigeria to the capital Abuja on July 24 – a week after the nose gear was installed.
After the ATR took off from Runway 05, employees of the airline’s ground handling company reported to the airport station manager that an object “was observed rolling off the aircraft,” according to the Nigerian Safety Investigation Bureau.
The aircraft continued on to Abuja, where it landed on runway 22 56 minutes after takeoff.
The crew noticed a “tendency to drift to the left” after touchdown and extended the roll-out to slow the ATR before exiting the aircraft. Ground crew on the domestic tarmac informed the crew of the missing left nose wheel after the aircraft had parked.
None of the 67 passengers and four crew members were injured.
While the search for the missing wheel was unsuccessful, a spacer for a nose gear was recovered in Ilorin.
The Safety Bureau states that the nose wheel assembly was installed on July 17 and no anomalies were found during subsequent inspections, including a 750-hour 1A test conducted the day before the Lagos event.
But when the nose wheel was replaced after the incident, “signs of axial play were found” on a self-locking nut, the statement said.
This nut came from the same batch as the nut installed before the incident.
“The batch was quarantined and a nut from a different batch was subsequently obtained,” the agency said. “The newly installed nut does not yet show any signs of axial play.”
It states that the ATR in question (5N-GAA) completed 62 flight cycles between the installation of the nose gear and the incident.
The investigation is ongoing and further tests will include metallurgical analyses of samples from the suspected batch of self-locking nuts.
Green Africa Airways has since tightened post-installation inspections of nose wheel assemblies and now requires double checking. In addition, the company has introduced additional pre-flight and pre-release inspections.
