Physics4me
Aerospace
- May 2, 2010
- 2
.
On certain aircraft, the DMNI-70 and DMNI-50 L-Band (ATC/DME) Antenna exhibit corrosion on the blade, moreso the top than the bottom on propjets. This is usually first noticeable as a small amount of blistering under the original paint.
Closer visual inspection can sometimes reveal blistering of paint around the edges of the plastic window which is covered by the top coat of paint. If this window is pulled out, there is usually extensive corrosion inside. Windows with extensive corrosion come out easily. These antennas should be discarded. If you pull the plastic wedge out from the blade you must replace the antenna as it cannot be put back and usually breaks.
It appears that the opportunity for corrosion to start in this area is presented when the outer paint coating of the blade, which is approx 0.010-0.020 in thickness, cracks at the plastic-metal interface allowing moisture to get into the crevice. Thus if this condition can be prevented, the life of the antenna can be extended significantly.
Notwithstanding that repainting at an appropriate time may arrest the onset of corrosion, total repainting is not supported by the manufacturer of the antenna as it can lead to undesirable loss tangents and changes in VSWR. Nevertheless, some paint touchups and the application of polyurethane tape may assist in delaying the onset of corrosion as a result of stone chips and wind ersosion, for instance.
For new antennas, warranty provisions typically prevent mechanics touching up antennas with paint resulting in premature failure outside the warranty period and then that expense is borne by the airline/owner.
For the DMNI-70 / DMNI-50 antennas, you might consider painting a small strip of clear 3M edge sealer around the edge of the plastic window, especially if small hairline cracks in the paint are starting to appear. If there is any paint blistering occurring at this interface, you should discard the antenna. Sanding the blistered paint doesn't give you access to the region behind the wedge as it is usually indicative of more extensive corrision within the blade.
(If anyone has further information on ATC/DME antenna paint repairs, please post your comment here.)
On certain aircraft, the DMNI-70 and DMNI-50 L-Band (ATC/DME) Antenna exhibit corrosion on the blade, moreso the top than the bottom on propjets. This is usually first noticeable as a small amount of blistering under the original paint.
Closer visual inspection can sometimes reveal blistering of paint around the edges of the plastic window which is covered by the top coat of paint. If this window is pulled out, there is usually extensive corrosion inside. Windows with extensive corrosion come out easily. These antennas should be discarded. If you pull the plastic wedge out from the blade you must replace the antenna as it cannot be put back and usually breaks.
It appears that the opportunity for corrosion to start in this area is presented when the outer paint coating of the blade, which is approx 0.010-0.020 in thickness, cracks at the plastic-metal interface allowing moisture to get into the crevice. Thus if this condition can be prevented, the life of the antenna can be extended significantly.
Notwithstanding that repainting at an appropriate time may arrest the onset of corrosion, total repainting is not supported by the manufacturer of the antenna as it can lead to undesirable loss tangents and changes in VSWR. Nevertheless, some paint touchups and the application of polyurethane tape may assist in delaying the onset of corrosion as a result of stone chips and wind ersosion, for instance.
For new antennas, warranty provisions typically prevent mechanics touching up antennas with paint resulting in premature failure outside the warranty period and then that expense is borne by the airline/owner.
For the DMNI-70 / DMNI-50 antennas, you might consider painting a small strip of clear 3M edge sealer around the edge of the plastic window, especially if small hairline cracks in the paint are starting to appear. If there is any paint blistering occurring at this interface, you should discard the antenna. Sanding the blistered paint doesn't give you access to the region behind the wedge as it is usually indicative of more extensive corrision within the blade.
(If anyone has further information on ATC/DME antenna paint repairs, please post your comment here.)
