Narrative:

During approach and landing in atl, numerous thunderstorm cells around. Worked through the gaps and got on final for runway 9R ILS about 15 mi out. Something (probably lightning or power surges) caused ILS signal to go out 3 or 4 times during the approach. Outage lasted 10-15 seconds each time. Wind caused drift problems when localizer was out. Aircraft were on parallel ILS to runway 8L and there was danger of getting too close to them whenever localizer was out. Unable to go around (which called for turn to south) because a big cell was located there. Had trouble communicating with approach because other aircraft on final had the same problem and had frequency tied up. Everything came out ok with safe landing, but was hectic which is not the way to operate aircraft. Maybe ATC should increase distance between aircraft and give more stagger between aircraft on parallel approachs when the WX is this bad. Callback conversation with reporter revealed the following information: the fluctuations in the localizer reception occurred at a very busy time of day at atl. There were several hundred aircraft in the vicinity. The problem was serious enough that the captain directed the engineer to scan to the north, to cover the approachs into runway 8. The clouds were broken and layered, giving visibility and other aircraft identify. It seemed unsafe to follow missed approach procedures because of the air and frequency congestion. The L-1011 had drifted from the localizer, and somewhere in the transmission a 'different voice' was heard, which vectored air carrier flight crew back onto the localizer. Captain has reported primarily out of certificate protection concerns, but states that this caught his attention. There were no more safety margins.

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Original NASA ASRS Text

Title: WHILE ON APCH NEAR TSTM ACTIVITY (WITH ASSOCIATED WINDS AND TURB), AN L-1011 FLC EXPERIENCED FLUCTUATIONS IN THE ILS DISPLAY, WHICH CAUSED DEVS FROM THE LOC.

Narrative: DURING APCH AND LNDG IN ATL, NUMEROUS TSTM CELLS AROUND. WORKED THROUGH THE GAPS AND GOT ON FINAL FOR RWY 9R ILS ABOUT 15 MI OUT. SOMETHING (PROBABLY LIGHTNING OR PWR SURGES) CAUSED ILS SIGNAL TO GO OUT 3 OR 4 TIMES DURING THE APCH. OUTAGE LASTED 10-15 SECONDS EACH TIME. WIND CAUSED DRIFT PROBS WHEN LOC WAS OUT. ACFT WERE ON PARALLEL ILS TO RWY 8L AND THERE WAS DANGER OF GETTING TOO CLOSE TO THEM WHENEVER LOC WAS OUT. UNABLE TO GAR (WHICH CALLED FOR TURN TO S) BECAUSE A BIG CELL WAS LOCATED THERE. HAD TROUBLE COMMUNICATING WITH APCH BECAUSE OTHER ACFT ON FINAL HAD THE SAME PROB AND HAD FREQ TIED UP. EVERYTHING CAME OUT OK WITH SAFE LNDG, BUT WAS HECTIC WHICH IS NOT THE WAY TO OPERATE ACFT. MAYBE ATC SHOULD INCREASE DISTANCE BTWN ACFT AND GIVE MORE STAGGER BTWN ACFT ON PARALLEL APCHS WHEN THE WX IS THIS BAD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FLUCTUATIONS IN THE LOC RECEPTION OCCURRED AT A VERY BUSY TIME OF DAY AT ATL. THERE WERE SEVERAL HUNDRED ACFT IN THE VICINITY. THE PROB WAS SERIOUS ENOUGH THAT THE CAPT DIRECTED THE ENGINEER TO SCAN TO THE N, TO COVER THE APCHS INTO RWY 8. THE CLOUDS WERE BROKEN AND LAYERED, GIVING VISIBILITY AND OTHER ACFT IDENT. IT SEEMED UNSAFE TO FOLLOW MISSED APCH PROCS BECAUSE OF THE AIR AND FREQ CONGESTION. THE L-1011 HAD DRIFTED FROM THE LOC, AND SOMEWHERE IN THE XMISSION A 'DIFFERENT VOICE' WAS HEARD, WHICH VECTORED ACR FLC BACK ONTO THE LOC. CAPT HAS RPTED PRIMARILY OUT OF CERTIFICATE PROTECTION CONCERNS, BUT STATES THAT THIS CAUGHT HIS ATTN. THERE WERE NO MORE SAFETY MARGINS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.