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An apparent miscom while wearing an oxygen mask ends with a descent to an altitude unexpected by ATC.
| Attributes | |
| ACN | 594939 |
| Time | |
| Date | 200309 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : szw.vortac |
| State Reference | FL |
| Altitude | msl bound lower : 33000 msl bound upper : 35000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zjx.artcc tower : tus.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B757 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : enroute altitude change |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 210 flight time total : 19000 flight time type : 3500 |
| ASRS Report | 594939 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | altitude deviation : overshoot non adherence : clearance |
| Independent Detector | other controllerb |
| Resolutory Action | controller : issued new clearance |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
En route to tampa, proceeding direct to the szw VOR at FL370, first officer had to use the restroom and left the cockpit. Captain put on oxygen mask and turned on speaker. Center cleared flight to FL330. Captain put FL330 in altitude window and replied 'FL330' to ATC. When level at FL330, ATC asked what our altitude was and we replied FL330. He stated he wanted FL350 and to remain at FL330. Reasons for situation: one pilot both receiving and responding to ATC. Use of oxygen mask (ATC probably received a garbled response). Use of speakers instead of headset. ATC can be hard to hear and understand. Corrective actions: extra vigilance while operating single pilot. Usually not that much time that the other pilot is out of the cockpit. Why not respond to ATC then ask for the clearance again and respond a second time?
Original NASA ASRS Text
Title: AN APPARENT MISCOM WHILE WEARING AN OXYGEN MASK ENDS WITH A DSCNT TO AN ALT UNEXPECTED BY ATC.
Narrative: ENRTE TO TAMPA, PROCEEDING DIRECT TO THE SZW VOR AT FL370, FO HAD TO USE THE RESTROOM AND LEFT THE COCKPIT. CAPT PUT ON OXYGEN MASK AND TURNED ON SPEAKER. CTR CLRED FLT TO FL330. CAPT PUT FL330 IN ALT WINDOW AND REPLIED 'FL330' TO ATC. WHEN LEVEL AT FL330, ATC ASKED WHAT OUR ALT WAS AND WE REPLIED FL330. HE STATED HE WANTED FL350 AND TO REMAIN AT FL330. REASONS FOR SIT: ONE PLT BOTH RECEIVING AND RESPONDING TO ATC. USE OF OXYGEN MASK (ATC PROBABLY RECEIVED A GARBLED RESPONSE). USE OF SPEAKERS INSTEAD OF HEADSET. ATC CAN BE HARD TO HEAR AND UNDERSTAND. CORRECTIVE ACTIONS: EXTRA VIGILANCE WHILE OPERATING SINGLE PLT. USUALLY NOT THAT MUCH TIME THAT THE OTHER PLT IS OUT OF THE COCKPIT. WHY NOT RESPOND TO ATC THEN ASK FOR THE CLRNC AGAIN AND RESPOND A SECOND TIME?
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.