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A B737-800 pilot is concerned that flying coupled ILS approaches in VMC may lead to excessive glide slope fluctuations because the ILS area is unprotected if ATC does not know it is in use by the approaching aircraft.
| Attributes | |
| ACN | 815370 |
| Time | |
| Date | 200812 |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : sea.airport |
| State Reference | WA |
| Altitude | msl single value : 1000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Dawn |
| Aircraft 1 | |
| Controlling Facilities | tower : sea.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-800 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | ils localizer & glide slope : i-snq |
| Flight Phase | descent : approach |
| Route In Use | approach : instrument precision |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Experience | flight time last 90 days : 120 flight time type : 2200 |
| ASRS Report | 815370 |
| Events | |
| Anomaly | other anomaly other |
| Independent Detector | other flight crewa |
| Resolutory Action | none taken : anomaly accepted |
| Supplementary | |
| Problem Areas | Airport Aircraft |
| Primary Problem | Ambiguous |
Narrative:
Approaching sea for a visual runway 16L in dawn lighting conditions. Flew hand flown visual following guidance from ILS runway 16L. Tower crossed aircraft downfield while we were at about 3000 ft with very little navigation disruption. When at about 900-1000 ft; tower crossed an aircraft over runway 16L to hold short runway 16C. No deviations noted as aircraft crossed runway; but when aircraft reached other side our GS had deviations up and down of no more than 3/4 of a DOT. With good WX the critical area was not protected. Aircraft that crossed was a dash 8-400 I think; but not positive on that. I believe that we need to immediately suspend any autoplt flown ILS approachs to runway 16L at sea when the WX is above 600 ft. The extra 200 ft in case ATC still doesn't protect the ILS critical area. At 800 ft GS issue runway 16L.
Original NASA ASRS Text
Title: A B737-800 PILOT IS CONCERNED THAT FLYING COUPLED ILS APPROACHES IN VMC MAY LEAD TO EXCESSIVE GLIDE SLOPE FLUCTUATIONS BECAUSE THE ILS AREA IS UNPROTECTED IF ATC DOES NOT KNOW IT IS IN USE BY THE APPROACHING AIRCRAFT.
Narrative: APCHING SEA FOR A VISUAL RWY 16L IN DAWN LIGHTING CONDITIONS. FLEW HAND FLOWN VISUAL FOLLOWING GUIDANCE FROM ILS RWY 16L. TWR CROSSED ACFT DOWNFIELD WHILE WE WERE AT ABOUT 3000 FT WITH VERY LITTLE NAV DISRUPTION. WHEN AT ABOUT 900-1000 FT; TWR CROSSED AN ACFT OVER RWY 16L TO HOLD SHORT RWY 16C. NO DEVS NOTED AS ACFT CROSSED RWY; BUT WHEN ACFT REACHED OTHER SIDE OUR GS HAD DEVS UP AND DOWN OF NO MORE THAN 3/4 OF A DOT. WITH GOOD WX THE CRITICAL AREA WAS NOT PROTECTED. ACFT THAT CROSSED WAS A DASH 8-400 I THINK; BUT NOT POSITIVE ON THAT. I BELIEVE THAT WE NEED TO IMMEDIATELY SUSPEND ANY AUTOPLT FLOWN ILS APCHS TO RWY 16L AT SEA WHEN THE WX IS ABOVE 600 FT. THE EXTRA 200 FT IN CASE ATC STILL DOESN'T PROTECT THE ILS CRITICAL AREA. AT 800 FT GS ISSUE RWY 16L.
Data retrieved from NASA's ASRS site as of May 2009 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.