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Conference & Report

FAA wire incidents report: March 2009

 ·  Lectromec Team

The following are the wire incidents reported in the FAA’s March 2009 Circular 43-16A – Alert Number 368.

Incident # 1

From the perspective of FAA Wire Incidents, a mechanic provides this excellent analysis of his customer's aircraft problems:

"The owner took off for some pattern work. (Since...) the weather had been cold and clear for several days he thought it perfect for touch-&-goes. On the downwind leg he began his normal landing check list—including checking the carburetor heat. After pulling (this heat control) 'ON' the engine died. He turned off carburetor heat and the engine restarted on its own without pilot input. He continued the pattern and gradually reapplied carburetor heat on base and final. On short final the engine died and the pilot glided to a safe touchdown just beyond the end of the runway. He was able to restart the engine and taxi back to parking without incident.

We looked at the engine...and found the Scat hose (model 150 & A150; 1970-77 parts manual; figure 56; sheet 2; item 29) coming from the front baffle down to the front of the exhaust shroud had filled with water. The installed hose is in the form of a 'J', and the bottom of this 'J' was full of water and ice.

In our damp climate we have noticed this before and usually ensure each scat hose has a drain hole in any low areas. Somehow this (particular) aircraft had been missed. We have found water and ice in similar installations on Cessna 150 and 172 series aircraft. Because of their location, the air intake scoops in the front baffle funnel rain water into the SCAT hose, (filling) the forward hose. Sometimes the water overflows the front hose and flows along the lower inside of the heater shroud, (attempting...) to also fill the carburetor heat box-to-right-shroud Scat hose (model 150 & A150; 1970-77 parts manual; figure 56; sheet 2; item 19). This results in the engine receiving a large slug of water or ice when the carburetor heat is applied. Whether the water is in a liquid or solid form depends on the duration of the flight and whether the heat of the operating engine has melted any ice that may have formed during periods of inactivity.

This is a dangerous condition during weather conditions when carburetor icing is a possibility. The pilot would (be prompted) to turn on the carburetor heat to clear any icing that may have formed through the normal induction system. Instead of getting warm air as expected, the engine would suddenly receive a small to very large burst of water or ice into the induction system that could instantly refreeze, plugging the induction system entirely. So far, we have not seen this happen.

We normally encounter this problem in warmer months when we receive more rain. Under those conditions the pilots notice a rough running engine when carburetor heat is applied, and turn the heat off before the water is fully removed—or (they opt) to continue with the heat (applied and the resulting engine roughness...)—until the water clears from the hose.

One way to check for this problem on any aircraft is to (examine) the scat tube reinforcing wire for rust in the lower areas. The occasional water build-up will cause these reinforcing wires to have more pronounced rust on the lower portions where water would sit on the wire wraps. Any aircraft showing abnormal wire deterioration in those areas should consider installing drain holes."

Incident # 2

An unidentified mechanic relates the following:

"(The aircraft was departing the field...) when he reported he lost substantial power to the left engine just after take off, and that the left low pressure fuel boost pump light on the aircraft annunciator panel illuminated. He (effected a safe landing at an airport) and called for aircraft maintenance. The aircraft technician on location could not find any problems with the engine during run-up other than the electric, low pressure fuel boost pump not supplying rated pressure. (Note: the electric, in-line low pressure boost pump is intended for flight above 15,000 feet MSL and can be deferred, as per our Part 91 MEL (minimum equipment list). The aircraft (initiated its take-off roll for departure...) when the left engine again lost power at (approximately) 40 knots airspeed. (Subsequent) trouble shooting of the engine fuel pump and fuel nozzles revealed no problems. The in-line low pressure fuel pump was removed (revealing) the bypass valve assembly in the pump had dislodged from the pump body and acted as a fuel (flow) restriction to the emergency electric fuel pump. We have been operating the Piper Navajo Chieftain aircraft for 20 years and have never seen this happen until now."

(Parker Hannifin Pump, P/N 2B6-64. Time since overhaul: 2,098.4 hours. The FAA Service Difficulty Reporting System (SDRS) reflects 11 entries for this part number.)

Incident # 3

(The following combines five reports on four PA32 aircraft—all from the same mechanic.)

This aircraft's "...main gear down lock switch wires pull tight on the strut during retraction, pulling wire strands apart to the breaking point. The silicone type wire coating tends to hold the wire ends together, creating intermitent contact. (This assembly) needs better wire and routing."

Incident # 4

Incident # 5

Incident # 6

Incident # 7

Incident # 8

Incident # 9

Incident # 10

Incident # 11

Incident # 12

Incident # 13

Incident # 14

Incident # 15

Incident # 16

Incident # 17

Incident # 18

Incident # 19

Incident # 20

Lectromec Team
Lectromec Team

This article was written by the Lectromec technical team. Aircraft wiring is our passion and we strive to make a contribution to the field by sharing our expertise through blogs, podcasts, and videos. We hope you find this information helpful. We also encourage you to submit comments and spur discussions.