Altitude deviation undershoot on descent.

Attributes
ACN	143707
Time
Date	199004
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : teb
State Reference	NJ
Altitude	msl bound lower : 2000 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 20 flight time total : 8500 flight time type : 30
ASRS Report	143707
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : undershoot conflict : airborne less severe non adherence : published procedure other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

PIC was conducting the VOR DME-a at teb using RNAV appeared to both of us to be programmed correctly. We thought we were outside wanes however approach told us to expedite to 2000 because of crossing traffic going into newark. I asked him how far he showed us from wanes and he said we were actually four mi from clifo, the final approach fix. Immediately I switched to the VOR mode and DME changed from 16.8 to 4.1 which meant we should have been at the mandatory 2000 instead of 3000. Told PF to immediately descend. We had the traffic in sight and I don't think there was a conflict, but it was a mandatory altitude. I always tell my students to never rely on one navigation source and it looks like I got caught.

Original NASA ASRS Text

Title: ALT DEVIATION UNDERSHOOT ON DESCENT.

Narrative: PIC WAS CONDUCTING THE VOR DME-A AT TEB USING RNAV APPEARED TO BOTH OF US TO BE PROGRAMMED CORRECTLY. WE THOUGHT WE WERE OUTSIDE WANES HOWEVER APCH TOLD US TO EXPEDITE TO 2000 BECAUSE OF XING TFC GOING INTO NEWARK. I ASKED HIM HOW FAR HE SHOWED US FROM WANES AND HE SAID WE WERE ACTUALLY FOUR MI FROM CLIFO, THE FINAL APCH FIX. IMMEDIATELY I SWITCHED TO THE VOR MODE AND DME CHANGED FROM 16.8 TO 4.1 WHICH MEANT WE SHOULD HAVE BEEN AT THE MANDATORY 2000 INSTEAD OF 3000. TOLD PF TO IMMEDIATELY DSND. WE HAD THE TFC IN SIGHT AND I DON'T THINK THERE WAS A CONFLICT, BUT IT WAS A MANDATORY ALT. I ALWAYS TELL MY STUDENTS TO NEVER RELY ON ONE NAV SOURCE AND IT LOOKS LIKE I GOT CAUGHT.

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.