Keeping Water Out

Water and electrons don't mix, and usually do so to the detriment of electrical systems, as recounted by the National Transportation Safety Board (NTSB) regarding water leaking in through the doorways of certain regional jets (see AM, May 2006, p. 42).

I am reminded of a similar problem we aircraft maintenance technicians at FedEx Express encounter while our main deck cargo doors and crew entry doors are open during rain or snow events while loading or unloading the aircraft of the freight containers.

The B-727 aircraft have the avionics and electrical equipment racks directly below the main cabin entry door area, so when it rains water will collect in this entry area and puddle. If this situation is allowed to persist, water could flow into the cockpit, and then the standing water in the entry area could migrate through the floor to the electrical and avionics racks below, causing all kinds of havoc.

On time flight schedules and time-sensitive package shipping is the essence of our business, so unless lightning is present, we continue the loading /unloading operations with the crew entry doors open, the main cargo door in the canopy position, and we contain the water that enters the aircraft by placing layers of absorbent mats on floor in the aircraft entryway (see photo #1). This proves to be a very effective method in containing the rain/wet snow that gets in the aircraft, and this also prevents puddling of the water in the entryway. When the mats are saturated, they are removed and dry mats are put in place. This solution is a quick and cost effective temporary solution to a serious problem.

We have also sealed the floors in the entry way in main cargo deck floors and installed drip shields over all avionics racks and electrical equipment racks (see photo #2). We used a fire resistant product called Gill Liner, and it comes in sheets. We at FedEx have had the edges strengthened by adding a slightly downward bent metal strip around the perimeter, then fastened the strip to floor support beams in the ceiling over the racks. By this means, any migrating water is deflected away from the racks of electronic equipment and to the aircraft drain points.

It is understood that the aircraft manufacturer mentioned in the earlier AM article is in the process of modify all the CRJ-200s with drip shields over the electronics and relay racks and sealing the floors of the entry way to the cabin and cockpit, but that takes aircraft down time and funding. In the meantime, the placement of the absorbent mats in the cabin entryway of these CRJ-200s and other aircraft during rain/wet snow could be one solution to prevent water that has come in to be contained and then removed quickly.

In fact, I have passed a recommendation to this effect to the Federal Aviation Administration (FAA) Flight Standards District Office (FSDO), as all operators need to be made aware of what can, and has, been done to contain and remove water from aircraft. It is critical that water not mix with the flow of electrons needed to power our flight instrument and computers required to fly the aircraft safely.

The only hazard to using the absorbent mats in the aircraft entryway is that a boarding passenger could trip or stumble while walking over the mats if not advised of their presence. But in the light of a more pressing requirement, of having the absorbents mats there in the first place, a diligent gate agent should be standing near the entry door to make the necessary reminders to folks entering or exiting the jet to take care when walking over the mats. Then, before departure, the gate agent could remove the saturated absorbent mats and discard them.

That's far preferable to a serious electrical problem in flight from water contamination of vital electrical circuits and components.

Roger Knight is a senior aircraft field line maintenance technician with FedEx at T.F. Green Airport, Warwick, R.I.