FAA Proposes Mandatory 737NG Stabilizer Inspections Following Reports of Dangerous "Pitch Oscillations"

WASHINGTON, D.C. — In a significant move to address emerging safety concerns within the global narrowbody fleet, the Federal Aviation Administration (FAA) officially issued a Notice of Proposed Rulemaking (NPRM) today, January 8th, 2026, targeting the horizontal stabiliser components of the Boeing 737 Next Generation (NG) series.

The proposed Airworthiness Directive (AD) comes after several carriers reported unsettling flight control anomalies, prompting a federal investigation into the structural integrity of the aircraft's pitch control system.

The "Free Play" Problem

The FAA's proposal is driven by technical reports from multiple airlines regarding “pitch oscillation events”, unintended and sudden movements of the aircraft's nose, during various phases of flight. Investigations pinpointed the cause as excessive free play in the horizontal stabiliser’s mechanical assembly.

According to the official FAA rule released this morning:

“The FAA has received reports from multiple operators of pitch oscillation events due to excessive horizontal stabiliser free play. Currently, there is no inspection requirement in place to address the wear of the left and right horizontal stabiliser pivot hinges and jackscrew.”

Key Components Under Scrutiny

The inspection focus is centred on two critical areas of the tail section that manage the aircraft's trim and pitch stability:

Pivot Hinges: The attachment points that allow the horizontal stabiliser to tilt.

Jackscrew Assembly: The primary screw-driven mechanism that modulates the stabiliser's angle to maintain level flight.

The "Flutter" Risk

Aerospace engineers warn that if left unchecked, the wear in these components can reach a threshold where the stabiliser is no longer held rigidly against aerodynamic forces. This lack of "stiffness" can trigger a flutter event, a high-frequency, self-excited vibration that can lead to rapid structural failure.

The FAA explicitly stated that the excessive stabiliser movement “could lead to a flutter event,” a scenario that historically has resulted in the loss of aircraft control.

Fleet Impact and Operator Requirements

The proposed mandate would encompass the entire US-registered 737NG fleet, totalling 1,987 aircraft.

This includes the following variants:

• 737-600
• 737-700 / -700C
• 737-800
• 737-900 / -900ER

Mandating the June 2025 Guidance

The FAA’s action seeks to codify and make mandatory a set of service instructions that Boeing initially distributed to airlines as optional guidance in June 2025. While some proactive carriers have already begun these checks, the new AD would ensure total fleet compliance under strict federal oversight.

The proposed requirements include:

Precision Measurement: Operators must measure the "free play value" of the left and right pivot hinges and the jackscrew.

Component Replacement: Any parts found to exceed the manufacturer’s specified wear limits must be replaced before further flight.

Repetitive Inspections: Establishing a recurring schedule to monitor wear progression over the aircraft's operational life.

Industry Response and Next Steps

Boeing has stated it is working closely with the FAA and its customers to ensure the "safety and integrity of the fleet." Major 737NG operators, including Southwest Airlines, United, and Delta, are currently reviewing the technical requirements of the proposal.

The FAA has opened a 45-day public comment period, allowing engineers, pilots, and airlines to provide feedback on the proposed inspection methods and compliance timelines. If the rule is finalised as expected, inspections could become mandatory for all US operators by late February or March 2026.