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A B727 fails to hold the ILS GS after an initial capture. Crew cites the design of the autoplt altitude hold switch as a factor.
| Attributes | |
| ACN | 396170 |
| Time | |
| Date | 199803 |
| Day | Sat |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : atl |
| State Reference | GA |
| Altitude | msl bound lower : 2350 msl bound upper : 2700 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : atl |
| Operator | common carrier : air carrier |
| Make Model Name | B727 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : approach descent other |
| Route In Use | approach : straight in arrival other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 6150 flight time type : 3340 |
| ASRS Report | 396170 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : instrument pilot : flight engineer pilot : commercial pilot : atp |
| Experience | flight time last 90 days : 530 flight time total : 16200 flight time type : 310 |
| ASRS Report | 396636 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : undershoot non adherence : published procedure |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course flight crew : overcame equipment problem |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation other |
Narrative:
The autoplt GS failed to capture in altitude hold. 'Clear to maintain 2700 ft and cleared for approach.' the aircraft descended to 2350 ft MSL at which time the PF manually corrected back to GS and continued the approach. Supplemental information from acn 396636: the block 4 B727 autoplt has a very poorly designed altitude hold switch that is difficult to see and does not contain an 'altitude captured' display.
Original NASA ASRS Text
Title: A B727 FAILS TO HOLD THE ILS GS AFTER AN INITIAL CAPTURE. CREW CITES THE DESIGN OF THE AUTOPLT ALT HOLD SWITCH AS A FACTOR.
Narrative: THE AUTOPLT GS FAILED TO CAPTURE IN ALT HOLD. 'CLR TO MAINTAIN 2700 FT AND CLRED FOR APCH.' THE ACFT DSNDED TO 2350 FT MSL AT WHICH TIME THE PF MANUALLY CORRECTED BACK TO GS AND CONTINUED THE APCH. SUPPLEMENTAL INFO FROM ACN 396636: THE BLOCK 4 B727 AUTOPLT HAS A VERY POORLY DESIGNED ALT HOLD SWITCH THAT IS DIFFICULT TO SEE AND DOES NOT CONTAIN AN 'ALT CAPTURED' DISPLAY.
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.