An air carrier DC9 flight crew descend below the GS intercept altitude while still outside of the OM. The autoplt system had defaulted to the vertical speed mode when it was activated and armed for intercept while below the GS and the captain did not recognize this.

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Attributes
ACN	386340
Time
Date	199711
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : day
State Reference	OH
Altitude	msl bound lower : 2600 msl bound upper : 3000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : day tower : pwm
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : vuq Other
Flight Phase	descent : approach landing : go around
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 180 flight time total : 2800 flight time type : 800
ASRS Report	386340
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : published procedure non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : became reoriented other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We had just received approach clearance and had joined the localizer outside the OM. We had not yet intercepted the GS and were above the minimum GS intercept altitude. The captain (PF) began a descent to minimum GS intercept altitude (at least I thought). As we approached the altitude, the captain did not appear to be leveling off. I announced that I was not receiving GS indications on my HSI and ADI. He immediately commanded a go around. We were revectored for the approach and landed without further incident. I believe part of the confusion on the captain's part was that he was hand flying when we initiated our descent toward GS intercept altitude. During this, he asked me to engage the autoplt and arm the ILS capture. Because he was beneath the GS at the time, the autoplt would remain in vertical speed mode until GS capture. Apparently he must have thought the autoplt captured. Better communications and choice of words on my part may have prevented the go around.

Original NASA ASRS Text

Title: AN ACR DC9 FLC DSND BELOW THE GS INTERCEPT ALT WHILE STILL OUTSIDE OF THE OM. THE AUTOPLT SYS HAD DEFAULTED TO THE VERT SPD MODE WHEN IT WAS ACTIVATED AND ARMED FOR INTERCEPT WHILE BELOW THE GS AND THE CAPT DID NOT RECOGNIZE THIS.

Narrative: WE HAD JUST RECEIVED APCH CLRNC AND HAD JOINED THE LOC OUTSIDE THE OM. WE HAD NOT YET INTERCEPTED THE GS AND WERE ABOVE THE MINIMUM GS INTERCEPT ALT. THE CAPT (PF) BEGAN A DSCNT TO MINIMUM GS INTERCEPT ALT (AT LEAST I THOUGHT). AS WE APCHED THE ALT, THE CAPT DID NOT APPEAR TO BE LEVELING OFF. I ANNOUNCED THAT I WAS NOT RECEIVING GS INDICATIONS ON MY HSI AND ADI. HE IMMEDIATELY COMMANDED A GAR. WE WERE REVECTORED FOR THE APCH AND LANDED WITHOUT FURTHER INCIDENT. I BELIEVE PART OF THE CONFUSION ON THE CAPT'S PART WAS THAT HE WAS HAND FLYING WHEN WE INITIATED OUR DSCNT TOWARD GS INTERCEPT ALT. DURING THIS, HE ASKED ME TO ENGAGE THE AUTOPLT AND ARM THE ILS CAPTURE. BECAUSE HE WAS BENEATH THE GS AT THE TIME, THE AUTOPLT WOULD REMAIN IN VERT SPD MODE UNTIL GS CAPTURE. APPARENTLY HE MUST HAVE THOUGHT THE AUTOPLT CAPTURED. BETTER COMS AND CHOICE OF WORDS ON MY PART MAY HAVE PREVENTED THE GAR.

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.