Last summer, Southwest tried to kill a rule that would have tightened up engine fan blade inspections

This week, Southwest flight 1380 lost an engine in midair when one of its fan-blades cracked; it was the second time in recent years that this happened to one of Southwest's Boeing 737s.

In September 2016, Southwest 3472 was forced to make an emergency landing due to an engine failure when one of its fan-blades cracked. The manufacturer, CFM, subsequently announced that its fan-blades could develop dangerous internal cracks and asked the National Transportation Safety Board to enact a rule requiring frequent ultrasonic checks of the blades to detect cracks before they could cause engine failures.

Southwest filed comments with the NTSB objecting to the proposal, saying that they have so many Boeing 737s that are prone to the fault and that this would present a hardship. They insisted that their own inspection regime was sufficient to detect cracks before they became serious.

One person died in this week's incident.

SWA does NOT support the CFM comment on reducing compliance time to 12 months. SWA estimates there are 732 engines in the SWA population. Compliance time of 18 months will be needed to schedule and complete the required ultrasonic inspections. CFM's risk assessment... did not take credit for the number of fan blades already inspected in the fleet and the findings rate. SWA requests this risk assessment be updated to make a more data-informed AD mandated compliance time.

Southwest Airlines protested airworthiness directive designed to prevent engine failures [Sean Gallagher/Ars Technica]