The FAA, bowing to broad industry opposition, will rescind its interpretation of a rule governing rest for airline mechanics, reverting to a more flexible view that both management and unions have long considered acceptable.

The agency delivered the news in a Dec. 26 letter to the Aeronautical Repair Station Association (ARSA), which spearheaded the challenge to an FAA interpretation made nearly three years ago.

At issue was the FAA’s definition of language in Part 121.377 that dictates how often mechanics must have days off. The rule calls for “each person performing maintenance or preventative maintenance” to be given time off “for a period of at least 24 consecutive hours during any seven consecutive days, or the equivalent thereof within anyone calendar month.”

Industry has long assumed the rule meant mechanics could be on duty for more than six straight days, so long as at least 24 consecutive hours of rest was provided for each six-day block worked in a given calendar month.

But in a May 2010 letter to repair station certificate holder Pratt & Whitney, the FAA said the rule should be read as requiring 24 hours of rest every seven days except in extreme cases, such as national emergencies or “other unusual occurrences.” The agency explained that a work schedule “that generally provides for an average of one day off over several weeks cannot be said to be ‘equivalent’ to the more specific standard requiring one day off out of every seven days.”

ARSA quickly responded with a letter objecting to the FAA’s interpretation, arguing that it ignored the rule’s “or the equivalent thereof” language. If the FAA wanted to make such a substantive change, ARSA argued, the agency needed to use the rulemaking process, and not simply issue a letter of interpretation.

In April 2011, the FAA took the issue to the public, asking for comments on its interpretation. A cross-section of industry sided with ARSA.

“The text of the regulation is straightforward, and employers and employees have relied on the flexibility designed into section 121.377 to safely and efficiently manage maintenance requirements for many years,” said Airlines For America in its comments.

The Transportation Workers Union (TWU) said the “pre-existing and long-standing interpretation of the regulation was correct,” adding that “there is no basis in the language of the regulation for an interpretation that would turn it into a one day off in seven only” rule. TWU added that the FAA should convey a working group to help address mechanic fatigue issues that the agency attempts to address in its interpretation.