With about 60% of mandatory inspections done, nothing pointing to a pressing CFM56-7B fleet-safety issue linked to fan-blade failure has turned up, the engine manufacturer reports.
"CFM technicians are overall very pleased with how the fan blades have been maintained by the airlines," a GE spokesman said. "No imminent safety concern with the fleet has been uncovered." GE and Safran are joint-venture partners in CFM56 manufacturer CFM International.
The inspection orders, issued by FAA and the European Aviation Safety Agency (EASA) April 20, give operators until May 10 to perform ultrasonic inspections on fan blades on engines with more than 30,000 total cycles. The affected population is about 600 engines, CFM said.
The next stage of checks, on engines with at least 20,000 cycles, covers about 2,500 engines and must be done before September. CFM also recommends initial inspections for all other CFM56-7Bs when they reach 20,000 cycles.
CFM recommended the inspections based on analysis of similar engine failures on Southwest Airlines Boeing 737-700s--one on August 27, 2016, and one this past April 17. In both cases, preliminary investigations concluded fan blades with fatigue cracks fractured in-flight. In both accidents, parts of the affected engine's cowling broke away, and debris damaged the aircraft. In this month's accident, debris broke a cabin window, and one passenger died.
The National Transportation Safety Board (NTSB) is investigating both accidents, but has not publicly linked them.
CFM's initial recommendations came via a March 2017 service bulletin (SB) and were later expanded. Following the most recent failure, CFM issued a third SB, which regulators used to shape their mandates.
EASA mandated CFM's most recent set of recommended actions, while FAA's directive focused on the highest-time engines. The U.S. agency is expected to issue a follow-up order covering the rest of the CFM56-7B fleet.
Several operators, including Southwest, used CFM's recommendations to initiate accelerated inspection schedules before last week's mandates. Southwest CEO Gary Kelly said on an April 26 earnings call that the carrier's preliminary inspection findings include "no cracks or fatigue."
Southwest decided within hours of the April 17 accident to fast-track planned inspections on its entire CFM56-7B fleet, which powers 703 737-700s and -800s. The carrier already was following CFM's 2017 recommendations, with plans to inspect its 35,500 CFM56-7B fan blades by the end of the year. It had checked about 17,000 of them before the accident. Those inspections turned up one cracked fan blade, in May 2017.
Immediately following this month's accident, Southwest moved its full-fleet inspection deadline up to May 17. It has inspected 8,500 more blades and is on track to meet its accelerated timeline, said COO Michael Van de Ven.
While preliminary inspection findings are not pointing to fleet-wide issues, evaluations have just begun. Blades are being removed during the checks—in some cases simply to replace older parts that will soon need refurbishment. If an ultrasonic check detects a concern, the blade is removed and put through a second non-destructive test. Any blade still exhibiting possible cracks will be torn apart and analyzed, meaning details on any findings could take months.
NTSB has not released any new factual information on this month's accident since April 19, and investigators continue to collect and analyze information. While most attention has focused on the fan blade, the extent of the damage triggered by the part's failure--including the lost cowling, fuselage damage and a shattered window--and the similarities to the August 2016 accident is of equal concern.
"The loss of the single blade inside [the engine] shouldn't have caused such dramatic impact," Van de Ven told analysts on the earnings call.