Altitude deviation. Overshoot on descent.

Attributes
ACN	145300
Time
Date	199005
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 10700 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tracon : pbi
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 2400
ASRS Report	145300
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 18000 flight time type : 2000
ASRS Report	145100
Events
Anomaly	altitude deviation : overshoot altitude deviation : crossing restriction not met non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The captain was flying a descent to cross 45 DME southwest of ord VOR at 11000'. At 12000' I said '12 for 11; it's armed'. 'Armed' refers to a capture mode annunciated on our FMA's. Using the vertical speed mode he continued his descent. At 11400' the 'arm' annunciation disappeared; I said 'it's not armed!' and pulled the altitude knob once again arming the capture mode. ATC called and said, 'xx slow to 250 KTS' I reached for the microphone to reply and noticed the 'arm' mode was missing again. I rearmed it again and replied 'xx slowing to 250 KTS'. At 11000' I said 'eleven! Eleven!' the descent continued to 10700'. The aural warning sounded 'altitude...altitude'. The captain punched off the autoplt at 10600' and climbed back to 11000' and said 'I thought we were cleared to 10000'!' the lack of crew interaction aggravated this situation since the captain had misunderstood the original clearance and had not acknowledged my callouts. In retrospect, the 'arm' annunciation was cancelled by his use of the vertical speed wheel during the 'capture' process; since this altitude capture 'arm' annunciation disappears on its own from time to time I did not equate his actions with the 'arm' drop off, I thought it was another anomaly on the system.

Original NASA ASRS Text

Title: ALT DEVIATION. OVERSHOOT ON DESCENT.

Narrative: THE CAPT WAS FLYING A DSNT TO CROSS 45 DME SW OF ORD VOR AT 11000'. AT 12000' I SAID '12 FOR 11; IT'S ARMED'. 'ARMED' REFERS TO A CAPTURE MODE ANNUNCIATED ON OUR FMA'S. USING THE VERT SPD MODE HE CONTINUED HIS DSNT. AT 11400' THE 'ARM' ANNUNCIATION DISAPPEARED; I SAID 'IT'S NOT ARMED!' AND PULLED THE ALT KNOB ONCE AGAIN ARMING THE CAPTURE MODE. ATC CALLED AND SAID, 'XX SLOW TO 250 KTS' I REACHED FOR THE MIKE TO REPLY AND NOTICED THE 'ARM' MODE WAS MISSING AGAIN. I REARMED IT AGAIN AND REPLIED 'XX SLOWING TO 250 KTS'. AT 11000' I SAID 'ELEVEN! ELEVEN!' THE DSNT CONTINUED TO 10700'. THE AURAL WARNING SOUNDED 'ALT...ALT'. THE CAPT PUNCHED OFF THE AUTOPLT AT 10600' AND CLBED BACK TO 11000' AND SAID 'I THOUGHT WE WERE CLRED TO 10000'!' THE LACK OF CREW INTERACTION AGGRAVATED THIS SITUATION SINCE THE CAPT HAD MISUNDERSTOOD THE ORIGINAL CLRNC AND HAD NOT ACKNOWLEDGED MY CALLOUTS. IN RETROSPECT, THE 'ARM' ANNUNCIATION WAS CANCELLED BY HIS USE OF THE VERT SPD WHEEL DURING THE 'CAPTURE' PROCESS; SINCE THIS ALT CAPTURE 'ARM' ANNUNCIATION DISAPPEARS ON ITS OWN FROM TIME TO TIME I DID NOT EQUATE HIS ACTIONS WITH THE 'ARM' DROP OFF, I THOUGHT IT WAS ANOTHER ANOMALY ON THE SYS.

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.