David Rosing

SEL-29-01 does not address other potential ignition sources in the gear pump circuit. 1) Albeit rare (but this AD addresses a rare event anyway) the motor ground could be loose, either at the bolted connection of the motor to the pump reservoir housing or the housing to the airframe chassis ground. I recommend you add a step to check that these fasteners are tightened securely. If not, a spark could be emitted here as well. 2) In the case of the 172 RG, the pump motor relay is on the firewall about a foot away from the power pack. The insulating boots on this relay (on my airplane) is a hard plastic/nylon thing that seems like it could become brittle and expose these terminals just like on the pump motor itself. I recommend that this be inspected for the proper terminal boot/nipple to ensure this remains insulated from the surrounding areas. 3) Then we have the age-old question of the remaining terminals in the circuit, namely the wire lead that attaches to the pump motor breaker at the instrument panel. All of those leads are wide open without any boots whatsoever. Actually, all the circuits at the breakers at the bus breaker bar are completely bare. This seems to be an accepted practice, but if one is going to implement an AD to check for an insulating boot at the motor and to ensure the contacts are secure on the motor, is it hypocritical to not check all the connections on that circuit to ensure they're tight? The motor draws a lot of amps, especially at motor stall when the gear locks (if anything this is the highest load on the electrical system at this moment) so any loose connection in the circuit could conceivably cause a spark. Recommend all connections in the high current circuit be checked for tightness.