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Flight crew of a CL604 descended below assigned altitude due to clearance misunderstanding resulting in descending below minimum obstruction clearance altitude.
| Attributes | |
| ACN | 497977 |
| Time | |
| Date | 200101 |
| Day | Sun |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : hpn.airport |
| State Reference | NY |
| Altitude | msl bound lower : 4700 msl bound upper : 6000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : n90.tracon |
| Operator | general aviation : corporate |
| Make Model Name | Challenger CL604 |
| Operating Under FAR Part | Part 91 |
| Navigation In Use | other |
| Flight Phase | descent : intermediate altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : corporate |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 80 flight time total : 13500 flight time type : 350 |
| ASRS Report | 497970 |
| Person 2 | |
| Affiliation | company : corporate |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 50 flight time total : 6000 flight time type : 400 |
| ASRS Report | 497970 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance other spatial deviation |
| Independent Detector | atc equipment other atc equipment : radar other controllera |
| Resolutory Action | controller : issued alert flight crew : returned to assigned altitude |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | other |
Narrative:
First officer, flying, heard clearance and PNF set up EFIS for the descent clearance he and I 'heard.' as I started down on autoplt, I noticed a ridge 10 or 20 NM ahead. It had just crossed my mind that our/my intended altitude of 2500 ft MSL would put our crossing altitude within 1000 ft of the ridge. Before I could question the clearance, center called and asked if we were still at 6000 ft. I clicked off autoplt and started back to 6000 ft. Were it not for visually seeing the ridge, I would not have questioned what I thought I heard. In a quick check of TCASII showed no traffic conflicts.
Original NASA ASRS Text
Title: FLC OF A CL604 DSNDED BELOW ASSIGNED ALT DUE TO CLRNC MISUNDERSTANDING RESULTING IN DSNDING BELOW MINIMUM OBSTRUCTION CLRNC ALT.
Narrative: FO, FLYING, HEARD CLRNC AND PNF SET UP EFIS FOR THE DSCNT CLRNC HE AND I 'HEARD.' AS I STARTED DOWN ON AUTOPLT, I NOTICED A RIDGE 10 OR 20 NM AHEAD. IT HAD JUST CROSSED MY MIND THAT OUR/MY INTENDED ALT OF 2500 FT MSL WOULD PUT OUR XING ALT WITHIN 1000 FT OF THE RIDGE. BEFORE I COULD QUESTION THE CLRNC, CTR CALLED AND ASKED IF WE WERE STILL AT 6000 FT. I CLICKED OFF AUTOPLT AND STARTED BACK TO 6000 FT. WERE IT NOT FOR VISUALLY SEEING THE RIDGE, I WOULD NOT HAVE QUESTIONED WHAT I THOUGHT I HEARD. IN A QUICK CHK OF TCASII SHOWED NO TFC CONFLICTS.
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.