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Medium large transport reduced airspeed when encountering turbulence, but didn't advise ATC thereby creating a potential loss of standard separation.
| Attributes | |
| ACN | 82784 |
| Time | |
| Date | 198802 |
| Day | Thu |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : hbu |
| State Reference | CO |
| Altitude | msl bound lower : 31000 msl bound upper : 31000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdv |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | Large Transport, Low Wing, 3 Turbojet Eng |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| ASRS Report | 82784 |
| Person 2 | |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | non adherence : clearance other anomaly |
| Independent Detector | atc equipment other atc equipment : unspecified other controllera |
| Resolutory Action | controller : issued new clearance other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
These 2 aircraft were placed about 10 mi in trail when the first aircraft encountered chop and turbulence. Medium large transport X reduced his airspeed by a factor of mach 10. This speed reduction was unannounced and unauthorized. Large transport Y did not reduce his speed at all when flying through the airspace which medium large transport X had flown through just 2 mins before. The problem was discovered when the difference in airspds was noticed, this speed was at times in excess of 100 KTS. 4 different control instructions were issued to both of these aircraft. Seconds after these instructions the C/a system was activated. Evasive action was not required and loss of ATC sep never occurred. It is not uncommon for aircraft flying through areas of WX to make slight deviations from present heading and airspeed west/O ATC approval. Pilots must be made aware that even though a deviation might seem slight it could have drastic consequences.
Original NASA ASRS Text
Title: MLG REDUCED AIRSPD WHEN ENCOUNTERING TURB, BUT DIDN'T ADVISE ATC THEREBY CREATING A POTENTIAL LOSS OF STANDARD SEPARATION.
Narrative: THESE 2 ACFT WERE PLACED ABOUT 10 MI IN TRAIL WHEN THE FIRST ACFT ENCOUNTERED CHOP AND TURB. MLG X REDUCED HIS AIRSPD BY A FACTOR OF MACH 10. THIS SPD REDUCTION WAS UNANNOUNCED AND UNAUTH. LGT Y DID NOT REDUCE HIS SPD AT ALL WHEN FLYING THROUGH THE AIRSPACE WHICH MLG X HAD FLOWN THROUGH JUST 2 MINS BEFORE. THE PROB WAS DISCOVERED WHEN THE DIFFERENCE IN AIRSPDS WAS NOTICED, THIS SPD WAS AT TIMES IN EXCESS OF 100 KTS. 4 DIFFERENT CTL INSTRUCTIONS WERE ISSUED TO BOTH OF THESE ACFT. SECONDS AFTER THESE INSTRUCTIONS THE C/A SYS WAS ACTIVATED. EVASIVE ACTION WAS NOT REQUIRED AND LOSS OF ATC SEP NEVER OCCURRED. IT IS NOT UNCOMMON FOR ACFT FLYING THROUGH AREAS OF WX TO MAKE SLIGHT DEVIATIONS FROM PRESENT HDG AND AIRSPD W/O ATC APPROVAL. PLTS MUST BE MADE AWARE THAT EVEN THOUGH A DEVIATION MIGHT SEEM SLIGHT IT COULD HAVE DRASTIC CONSEQUENCES.
Data retrieved from NASA's ASRS site as of August 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.