View Full Version : Loss of Loc signal on EFIS with heavy precip.

30th Aug 2002, 11:55
This has happened to me three times so far. The first one was in a B-737-300 in Syracuse during a heck of a snowstorm in 1994; the other two times, it happened in Asia on B-737-800 aircraft while approaching in typhoon affected airports. What happens is that some where between 1600 feet AAL and 800 feet the localizer display on the PFD disappears while the standby gyro LOC indication remains normal. On the first time, I went around and held for about 10 minutes and on the second attempt, everything stayed normal. On the other two times, I was able to continue since I had the approach lights in sight. At the time the Syracuse event hapened, our avionics engineer at the time told me that it was a probable ground signal at the antenna instalation. So far in Asia, nobody has been able to give me a technical reason for it. Has this event occured to you, and if so, did you get any technical explanation for it?

30th Aug 2002, 13:55
Ive flown in some heavey wx in SEA but Ive never had the LLZ bars fizzle out on the 737-300 TV screens yet. Normaly they wink at 1500 RA during the test but of course it is to say it cant happen. Probabley due to moisture entering the equipment bay somehow and affecting the SG componant of the flt management computer itself, or the internal self-test itself screwed up. Can happen when the rains heavey enough to register on the radio alts.

30th Aug 2002, 16:22

On a related note, have there been any more problems with the CFM56's at approach idle during heavy rain? You remember the forced landing a 738 had to make (more of a controlled crash really) during an approach in a monsoon... have there been any AD's or company ops changes relating to this? Granted I'm not on the 738, but I'm curious to find out!