An air carrier flight crew overshot their assigned altitude during the descent. The altimeters had b...

Attributes
ACN	331819
Time
Date	199603
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ott
State Reference	MD
Altitude	msl bound lower : 14600 msl bound upper : 15000
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : zdc
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 250 flight time total : 7500 flight time type : 2000
ASRS Report	331819
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera 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:

During descent into phl (flight was from dfw) on the dupont 3 arrival. Clearance was to cross jaybo intersection at 15000 ft MSL. At 18000 ft, transition altitude, all 3 altimeters (captain, first officer's and middle altimeter) were set to 29.40 inches. As the captain was setting the altimeter he said '39?' and I said 'no, 40, 29.40 inches.' the aircraft was hooked up to the autoplt and somewhere between 16000 ft and 15000 ft (1000 ft above level off) the captain began spinning the center altimeter barometric knob first one way and then the other. I was flying the aircraft and with the center altimeter as my main instrument for xchk for altitude level off, the autoplt went through 15000 ft down to 14600 ft when the captain had spun the barometric knob up and down in confusion. The barometric altimeter settings were correct at 18000 ft, set for local 29.40 inches, but somewhere during descent from the transition altitude to passing 16000 ft and on down to 15000 ft, the captain was distracted and had reset the center altimeter to 30.40 inches (this also happened to be what our altimeter setting was when we left dfw). Perhaps cockpit discussions were distracting enough to cause the confusion between settings 29.40 inches and 30.40 inches. Also, the captain seemed concerned throughout the flight that he was coming back on his first trip after 9 weeks absence due to both vacation and sick leave. At an actual altitude of 14600 ft MSL the phl controller brought actual altitude to our attention and the aircraft was climbed to immediate level off at 15000 ft. I think that sometimes the altimeter procedures we have at our airline (which has the captain and the first officer setting a conversion altimeter below 10000 ft to QFE and the middle one to qnh) can be additionally confusing in an already distracting and complex flying environment. Perhaps a personal practice of sterile cockpit below 18000 ft instead of below 10000 ft is also advisable.

Original NASA ASRS Text

Title: AN ACR FLC OVERSHOT THEIR ASSIGNED ALT DURING THE DSCNT. THE ALTIMETERS HAD BEEN SET CORRECTLY, BUT THE CONFUSION THAT AROSE ABOUT THE CORRECT SETTING, AT LESS THAN 1000 FT ABOVE THE LEVEL OFF ALT, LED TO AN OVERSHOOT.

Narrative: DURING DSCNT INTO PHL (FLT WAS FROM DFW) ON THE DUPONT 3 ARR. CLRNC WAS TO CROSS JAYBO INTXN AT 15000 FT MSL. AT 18000 FT, TRANSITION ALT, ALL 3 ALTIMETERS (CAPT, FO'S AND MIDDLE ALTIMETER) WERE SET TO 29.40 INCHES. AS THE CAPT WAS SETTING THE ALTIMETER HE SAID '39?' AND I SAID 'NO, 40, 29.40 INCHES.' THE ACFT WAS HOOKED UP TO THE AUTOPLT AND SOMEWHERE BTWN 16000 FT AND 15000 FT (1000 FT ABOVE LEVEL OFF) THE CAPT BEGAN SPINNING THE CTR ALTIMETER BAROMETRIC KNOB FIRST ONE WAY AND THEN THE OTHER. I WAS FLYING THE ACFT AND WITH THE CTR ALTIMETER AS MY MAIN INST FOR XCHK FOR ALT LEVEL OFF, THE AUTOPLT WENT THROUGH 15000 FT DOWN TO 14600 FT WHEN THE CAPT HAD SPUN THE BAROMETRIC KNOB UP AND DOWN IN CONFUSION. THE BAROMETRIC ALTIMETER SETTINGS WERE CORRECT AT 18000 FT, SET FOR LCL 29.40 INCHES, BUT SOMEWHERE DURING DSCNT FROM THE TRANSITION ALT TO PASSING 16000 FT AND ON DOWN TO 15000 FT, THE CAPT WAS DISTRACTED AND HAD RESET THE CTR ALTIMETER TO 30.40 INCHES (THIS ALSO HAPPENED TO BE WHAT OUR ALTIMETER SETTING WAS WHEN WE LEFT DFW). PERHAPS COCKPIT DISCUSSIONS WERE DISTRACTING ENOUGH TO CAUSE THE CONFUSION BTWN SETTINGS 29.40 INCHES AND 30.40 INCHES. ALSO, THE CAPT SEEMED CONCERNED THROUGHOUT THE FLT THAT HE WAS COMING BACK ON HIS FIRST TRIP AFTER 9 WKS ABSENCE DUE TO BOTH VACATION AND SICK LEAVE. AT AN ACTUAL ALT OF 14600 FT MSL THE PHL CTLR BROUGHT ACTUAL ALT TO OUR ATTN AND THE ACFT WAS CLBED TO IMMEDIATE LEVEL OFF AT 15000 FT. I THINK THAT SOMETIMES THE ALTIMETER PROCS WE HAVE AT OUR AIRLINE (WHICH HAS THE CAPT AND THE FO SETTING A CONVERSION ALTIMETER BELOW 10000 FT TO QFE AND THE MIDDLE ONE TO QNH) CAN BE ADDITIONALLY CONFUSING IN AN ALREADY DISTRACTING AND COMPLEX FLYING ENVIRONMENT. PERHAPS A PERSONAL PRACTICE OF STERILE COCKPIT BELOW 18000 FT INSTEAD OF BELOW 10000 FT IS ALSO ADVISABLE.

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.

An air carrier flight crew overshot their assigned altitude during the descent. The altimeters had been set correctly, but the confusion that arose about the correct setting, at less than 1000 ft above the level off altitude, led to an overshoot.