(Corrects spelling of name from Mark Rosekind to Mark Rosenker in paragraph 25)
* Southwest had said airlines needed 18 months for inspections
* Carriers not required to track engine fan blades
* FAA to finalize inspection order within two weeks
By Tim Hepher and David Shepardson
April 19 (Reuters) - Southwest Airlines Co clashed with engine maker CFM over the timing of proposed inspections and with regulators over costs after a 2016 accident involving the airline that was caused by a fan blade separating, public documents showed.
The documents, which are on a U.S. federal website and were viewed by Reuters, reveal the wrangling over previously proposed safety checks on CFM engines that are now the focus of investigations following a fatal engine explosion this week.
The U.S. Federal Aviation Administration said on Wednesday it would order the inspection of some CFM jet engines after investigators said a broken fan blade touched off an engine explosion on a Southwest Airlines flight, shattering a window and killing a passenger. It was the first death in a U.S. commercial aviation accident since 2009.
In August 2016, a Southwest flight made a safe emergency landing in Florida after a fan blade separated from the same type of engine, and debris ripped a foot-long hole above the left wing. Investigators found signs of metal fatigue.
The Dallas-based carrier was not the only operator to ask for more time or suggest other changes as first the engine maker, CFM International, and then the FAA and its European counterpart proposed checks last year for potentially flawed fan blades.
CFM suggested a shorter examination period than some airlines wanted, of no more than 12 months. Southwest told the FAA in October that airlines needed 18 months and that only certain fan blades should be inspected, not all 24 in engines.
"SWA does NOT support the CFM comment on reducing compliance time to 12 months," Southwest Airlines wrote in a comment available on the federal website that allows companies and individuals to comment on proposed new rules. CFM International is a joint venture of General Electric and France's Safran.
The objections from Southwest and other airlines stem partly from the fact that carriers, while highly regulated, are not required to track each individual fan blade within an engine.
That, in turn, is making it harder for investigators to be certain whether the engine that exploded on a Boeing 737 on Tuesday was part of a group being targeted for inspection, according to the National Transportation Safety Board (NTSB).
The blades, which sweep air backwards to help provide thrust, can be changed and repaired independently of the rest of the engine, meaning airlines that don't keep tabs have to examine more engines than anticipated, which adds time and cost.
The NTSB said of Tuesday's incident that one of the fan blades on Southwest Flight 1380 broke and fatigue cracks were found on the inside of the blade.
Southwest said in its submission on the federal website it would have to inspect some 732 engines in one of two categories of engines under review - much higher than the FAA's total estimate of 220 engines needing to be inspected across the whole U.S. fleet.
"The affected engine count for the fleet in costs of compliance … appears to be vastly understated," it said.
Southwest did not immediately respond to an email requesting comment and an answering machine in its press office referred reporters to the company's website for all accident queries. On Tuesday, the airline said it would accelerate inspections and complete them in the next 30 days.
Other airlines commenting on last year's FAA proposal projected higher costs in time and money than regulators initially expected, because they did not closely track the fan blade.
American Airlines said fan blades in the engines that were of concern had been swapped out with those in similar engines. "Fan blades have been removed, repaired, reworked, and then relocated," it said, asking for 20 months to complete checks. "Although the number of fan blades requiring the inspection remains the same, the number of engines involved with this inspection has significantly increased," it said.
United Continental Holdings Inc made a similar argument. "The maintenance burden and cost for operators to inspect all effective fan blades is much more significant than proposed," it said.
United and American representatives were not available for comment after hours on Wednesday.
Safety checks in Europe have also been contentious.
European regulators last month ordered checks within just nine months of April 2, following the 2016 engine incident at Southwest, although investigators warn it is too early to say whether the two problems are linked.
The FAA said on Wednesday it would finalize the airworthiness directive it had proposed in August within two weeks. It will require inspections of some CFM56-7B engines, the type on the Southwest flight, and FAA officials acknowledged the total number of engines could be higher than the 220 initially estimated.
But regulators face questions over the speed of their response to the Southwest jet's 2016 engine blowout.
Former NTSB chairman Mark Rosenker said in an interview the safety board will look at why the FAA had not already mandated the inspections that it had proposed in August 2017.
"There did not seem to be an urgency" at the FAA to finalize the inspections, he said.
The FAA wasn't immediately available for comment. (Additional reporting by Jamie Freed, Editing by Peter Henderson and Muralikumar Anantharaman)