Summary
The FAA proposes to adopt a new airworthiness directive (AD) for all Boeing Model 707, 720, and 720B series airplanes. This proposed AD would require revising the Limitations section of the airplane flight manual (AFM). The AFM revisions include instructions for monitoring the low pressure lights for the center tank fuel pumps, and a statement prohibiting the resetting of a tripped circuit breaker for a fuel pump in any tank. This proposed AD is prompted by the results of fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent dry operation of the fuel pumps in the center fuel tank, which could result in high temperatures or sparks inside the fuel tank, ignition of fuel vapors, and consequent fire or explosion. We are also issuing this AD to prohibit the resetting of a tripped circuit breaker for a fuel pump in any tank, which could allow an electrical fault to override the protective features of the circuit breaker, and result in sparks inside the fuel tank, ignition of fuel vapors, and consequent fire or explosion.