Concern about fire suppression has led the Federal Aviation Administration to prohibit airlines from carrying cargo in the aft holds of Boeing 737s that have failed air conditioning airflow systems.

The FAA issued the prohibition – which affects 737 Max 8s, Max 9s, 737-800s and 737-900ERs – in a 5 August airworthiness directive (AD).

Boeing calls the issue a “potential condition” that would only be problematic if a sequence of events occurred.

“We have not seen it occur in service,” Boeing adds. “This proactive approach to raising and addressing potential safety issues has helped make commercial aviation the world’s safest form of transportation.”

As of 19 August, operators may not “dispatch or release an airplane with cargo in the aft cargo compartment with failed electric flow control of air conditioning packs,” says the AD.

American 737 Max-c-American Airlines

Source: American Airlines

Operators can dispatch the jets if the aft compartments are empty.

The FAA issued the order after learning that “aft cargo compartment fire suppression capability is reduced on affected airplanes if the airplane is dispatched or released with failed electronic flow control of air conditioning packs,” the order says.

Failed flow controls “significantly increase the pack airflow and cargo compartment air leakage”, which could “result in insufficient concentration of Halon fire suppressant in the aft cargo compartment”.

Boeing notified the FAA of the issue in March. The company could not immediately be reached for comment.

Story updated on 6 August to include a comment from Boeing.