Nigerian investigators have isolated a batch of self-locking nuts for analysis after a Green Africa Airways ATR 72-600 suffered the loss of a nose-wheel during take-off.
The aircraft had been operating a service from Ilorin, in western Nigeria, to the capital Abuja on 24 July – one week after the nose-gear assembly was installed.
After the ATR lifted off from runway 05, personnel from the carrier’s ground-handling company reported to the airport’s station manager that an object “was observed rolling off the aircraft”, states the Nigerian Safety Investigation Bureau.
The aircraft continued to Abuja where, 56min after taking off, it landed on runway 22.
Its crew noted a “tendency to veer left” after touchdown and extended the roll-out to slow the ATR before vacating. Ground staff at the domestic apron notified the crew of the missing left-hand nose-wheel after the aircraft parked.
None of the 67 passengers and four crew members was injured.
While a search for the missing wheel has been unsuccessful, a nose-gear wheel spacer was recovered from Ilorin.
The safety bureau says the nose-wheel assembly was installed on 17 July, and no anomalies were detected during subsequent inspections, including a 750h 1A-check conducted at Lagos the day before the event.
But when the nose-wheel assembly was replaced after the incident, a self-locking nut was “observed to have shown signs of axial play”, it states.
This nut had been drawn from the same batch as the nut which was fitted prior to the occurrence.
“The batch was quarantined, and a nut was subsequently sourced from a different batch,” says the bureau. “The newly-installed nut has yet to show signs of axial play.”
It states that the ATR involved (5N-GAA) had undergone 62 flight cycles between the nose-gear installation and the incident.
The inquiry is continuing, and further investigation will include metallurgical analysis of samples from the suspect batch of self-locking nuts.
Green Africa Airways has since tightened post-installation inspections of nose-wheel assemblies, requiring a duplicate check, as well as introducing additional pre-flight and turnaround inspections.
