Altitude deviation.

Attributes
ACN	290025
Time
Date	199411
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : acv
State Reference	CA
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air carrier
Make Model Name	Jetstream 31
Operating Under FAR Part	Part 135
Flight Phase	descent : approach descent other landing other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 190 flight time total : 2700 flight time type : 190
ASRS Report	296025
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The jetstream 3100 has a DME readout with 4 buttons (DME, KTS, time, timer) the buttons do not remain depressed when a specific mode is selected and the readout does not indicate whether you are in distance, time, or KTS. The only way to know the mode being displayed is to push the button especially between 'DME' and 'time' modes. I was the PF. My copilot pushed 'time' to assure that his call to our base operations was accurate. He never pushed it back to the DME mode. I began a VOR DME 14 approach to arcata. Thinking that I was inside 'wheel' intersection, I started my descent based on what I thought I was an indication of less than 10.8 DME. However, the readout was actually indicating 'min to the station.' I was actually over 22 NM out and started down way too early. ZSE caught our mistake before we did. Chain of events: how the problem arose: switchology. Contributing factors: deceiving to the point of deceptive readout display. How it was discovered: ZSE query. Corrective actions: part of my instrument approach brief from now on. Human factors: due to direct routing and complacency both my copilot and myself failed to perceive the proper distance from arcata during a crucial phase of flight (ie, poor situational awareness).

Original NASA ASRS Text

Title: ALTDEV.

Narrative: THE JETSTREAM 3100 HAS A DME READOUT WITH 4 BUTTONS (DME, KTS, TIME, TIMER) THE BUTTONS DO NOT REMAIN DEPRESSED WHEN A SPECIFIC MODE IS SELECTED AND THE READOUT DOES NOT INDICATE WHETHER YOU ARE IN DISTANCE, TIME, OR KTS. THE ONLY WAY TO KNOW THE MODE BEING DISPLAYED IS TO PUSH THE BUTTON ESPECIALLY BTWN 'DME' AND 'TIME' MODES. I WAS THE PF. MY COPLT PUSHED 'TIME' TO ASSURE THAT HIS CALL TO OUR BASE OPS WAS ACCURATE. HE NEVER PUSHED IT BACK TO THE DME MODE. I BEGAN A VOR DME 14 APCH TO ARCATA. THINKING THAT I WAS INSIDE 'WHEEL' INTXN, I STARTED MY DSCNT BASED ON WHAT I THOUGHT I WAS AN INDICATION OF LESS THAN 10.8 DME. HOWEVER, THE READOUT WAS ACTUALLY INDICATING 'MIN TO THE STATION.' I WAS ACTUALLY OVER 22 NM OUT AND STARTED DOWN WAY TOO EARLY. ZSE CAUGHT OUR MISTAKE BEFORE WE DID. CHAIN OF EVENTS: HOW THE PROB AROSE: SWITCHOLOGY. CONTRIBUTING FACTORS: DECEIVING TO THE POINT OF DECEPTIVE READOUT DISPLAY. HOW IT WAS DISCOVERED: ZSE QUERY. CORRECTIVE ACTIONS: PART OF MY INST APCH BRIEF FROM NOW ON. HUMAN FACTORS: DUE TO DIRECT RTING AND COMPLACENCY BOTH MY COPLT AND MYSELF FAILED TO PERCEIVE THE PROPER DISTANCE FROM ARCATA DURING A CRUCIAL PHASE OF FLT (IE, POOR SITUATIONAL AWARENESS).

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.