Potential For Disengagement Of The Fuel Control Switch Locking Feature Discovered

The FAA has issued a Special Airworthiness Information Bulletin (SAIB) covering most of the airplanes manufactured by Boeing stemming from the discovery of the potential for disengagement of the fuel control switch locking feature.

Boeing received reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The fuel control switches (or engine start switches) are installed on the control stand in the flight deck and used by the pilot to supply or cutoff fuel to the engines. The fuel control switch has a locking feature to prevent inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cutoff positions. In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position.

If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown. Boeing informed the FAA that the fuel control switch design, including the locking feature, is similar on various Boeing airplane models.

The FAA recommends that all owners and operators of the affected airplanes incorporate the following actions at the earliest opportunity:

• Inspect the locking feature of the fuel control switch to ensure its engagement. While the airplane is on the ground, check whether the fuel control switch can be moved between the two positions without lifting up the switch. If the switch can be moved without lifting it up, the locking feature has been disengaged and the switch should be replaced at the earliest opportunity.

For Boeing Model 737-700, -700C, -800, and -900ER series airplanes and Boeing Model 737- 8 and -9 airplanes delivered with a fuel control switch having P/N 766AT613-3D: Replace the fuel control switch with a switch having P/N 766AT614-3D, which includes an improved locking feature.

(Source: FAA. Image from file)

FMI: SAIB