On 1 April 2016, ADS stated it was addressing production faults affecting 14 propeller gear boxes (PGBs) produced by Italian supplier Avio Aero in early 2015. The issue, involving a heat treatment process that weakened the ring gear, affected no other PGBs; the units involved needed changing. Airbus noted: "pending full replacement of the batch, any aircraft can continue to fly with no more than one affected propeller gear box installed and is subject to continuing inspections." Another PGB issue involved input pinion plug cracking, which could release small metallic particles into the oil system, which is safeguarded by a magnetic sensor; only engines 1 and 3, which have propellers that rotate to the right, are affected. The European Aviation Safety Agency (EASA) issued an Airworthiness Directive mandating immediate on-wing inspection, followed by replacement if evidence of damage is found. On 27 April 2016, Airbus warned there may be a substantial PGB repair cost. An interim PGB fix was certified in July 2016, greatly extending inspection intervals.