The FAA wants the tails of 1,987 American Boeing 737s measured for play that could end in flutter

The Federal Aviation Administration has ordered operators of 1,987 U.S.-registered Boeing 737 airplanes to measure how much their horizontal stabilizers can wiggle, because excess movement in that part of the tail has been tied to pitch oscillation events. The agency’s stated worry is flutter, a self-reinforcing vibration that, in its words, “can result in loss of control of the airplane.” The order covers the older 737 Next Generation family, not the 737 MAX.

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Which 737s, and what gets measured

The directive covers the 737-600, -700, -700C, -800, -900 and -900ER. Those are the models that preceded the MAX and that still fly in large numbers for U.S. carriers, and the FAA counts 1,987 of them on the U.S. register. Because the family is so widespread, a single tail-section inspection touches many fleets at once.

The text appeared in the Federal Register on October 19 and spells out the airplanes affected, the trigger and the unsafe condition the agency wants prevented.

According to the Federal Register’s record of the rule, operators must measure freeplay, the looseness in the mechanism that holds and positions the stabilizer. The checks cover the pivot hinges and the jackscrew, the threaded shaft that moves the stabilizer to trim the airplane’s pitch. Depending on the readings, operators then calculate total freeplay, repeat measurements and repair or replace worn parts.

The rule is formally AD 2026-20-14, filed under docket FAA-2025-5403, and it takes effect November 23, 2026. Until that date nothing in it is yet enforceable, so the first measurements are still weeks away and every compliance deadline is calculated forward from that day. The Federal Register entry also records that the FAA responded to the formal comments it received on the January 2026 proposal before finalizing the text.

The flutter risk the FAA describes

The trigger was operator reports. The FAA wrote that it received accounts of “pitch oscillation events due to excessive horizontal stabilizer freeplay,” and concluded that leaving the condition alone “could lead to a flutter event, which can result in loss of control of the airplane.”

The directive does not say how many such events occurred, when, or on which airlines, according to AeroCorner’s reading of the text. Nor does it cite an accident. That matters for how the order should be read: it is a preventive inspection requirement aimed at a measured wear condition, and the FAA has not said the airplanes are unsafe to fly while they wait for their checks. The same write-up notes that, before this rule, no inspection requirement existed for wear in these components.

That gap is why a jackscrew in a tail draws attention. The National Transportation Safety Board’s investigation of Alaska Airlines Flight 261 in 2000 involved worn jackscrew threads on a different airplane, an MD-83. The 737 directive itself does not mention that accident; the comparison comes from analysts, not from the FAA.

What it costs, and who pushed back

The FAA put the cost of one measurement at six work-hours at $85 an hour, or $510 per airplane. Across the 1,987 jets, that comes to $1,013,370 for the initial measurement alone. Repairs are a separate matter: the agency told commenters it had “received no definitive data” on what worn parts would cost, so no repair figure is included.

Several airlines asked for more room. As summarized by AeroCorner, Canadian North asked to stretch the first check from 12 months to 36, and United asked for longer repeat intervals on jets fitted with new hinge bearings. The FAA refused both. Alaska Airlines asked to repair worn parts at once instead of doing an interim check; the agency replied that an operator may perform the interim check early and make repairs in the same visit.

The Air Line Pilots Association, Boeing and two individuals supported the proposal as written. The FAA adopted it with minor editorial changes, and it says operators can ask to use an alternative method of compliance if they can supply supporting data.

The clock that starts in November

The work follows Boeing Alert Requirements Bulletin 737-55A1104 RB, issued June 12, 2025. The directive keeps the bulletin’s compliance times but counts them from the November 23 effective date instead of the bulletin’s own issue date, so operators do not get credit for the months since the bulletin appeared. After any repair, an airplane must pass a new check showing freeplay within the manufacturer’s limits before it returns to service.

For passengers, the practical effect is likely to be invisible: a few hours of hangar time per aircraft, scheduled into maintenance. The open question is what the first round of measurements will show. The FAA has published a cost for looking but none for fixing, and the scale of any repair work will only become clear once operators begin reporting what they find in 1,987 tails.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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