Boeing 787 that had not yet flown was found to have an indication of a similar crack on the fan midshaft. The fan midshaft was removed from the engine for further inspection and examination. As a result of investigative work the NTSB has determined that the fan midshafts on the GEnx engines fractured or cracked at the forward end of the shaft where the retaining nut is installed. On September 11, 2012, an AirBridgeCargo 747-8F experienced a major engine malfunction that spread a significant amount of metallic debris on the runway when the low-pressure turbine shaft separated and shifted backwards, damaging the low pressure turbine blades and vanes. The NTSB issued urgent safety recommendations to the FAA to require ultrasonic scans for midshaft fractures before use of GEnx engines and require repetitive on-wing inspections of the engine to detect cracks. During the spring and summer of 2013, GE learned of four 747-8F freighters that suffered icing in their engines at altitudes of and above. The most serious incident involved an AirBridgeCargo freighter; on July 31, while at an altitude of over China, the flight crew noted two engines surging while a third lost substantial power. The pilots were able to land the plane safely but the engines were found to have sustained damage. Among the possible factors cited was "'unique convective weather systems' such as unusually large thunderstorms reaching high altitudes." Boeing is working with GE on software solutions to the problem. Altitude was restricted until GE changed the software to detect the high-altitude ice crystals and open bleed air valve doors to eject them before they enter the core. In March 2014, a GEnx-powered Boeing 787 had its first in-flight shut down in operation when a JAL flight had to divert to Honolulu after an oil pressure alert, bringing its in-flight shut down rate to 1 per ,000 hours. In January 2016 a Japan Airlines 787 had an inflight shutdown after flying through icing conditions, caused by ice formed on fan blades and ingested: the blades moved forward slightly and rubbed on the abradable seal in the casing. In March 2016, the US FAA ordered emergency fixes on the GEnx-1B PIP2. The airworthiness directive affects 43 Boeing 787 Dreamliners in the US. Abradable material in the casing in front of the fan blades was ground to keep them from rubbing when ingesting ice or debris on 330 GEnx PIP-2.