Altitude deviation altitude excursion.

Attributes
ACN	299955
Time
Date	199503
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : thx
State Reference	TX
Altitude	msl bound lower : 27000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	general aviation : corporate
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 57 flight time total : 4548 flight time type : 764
ASRS Report	299955
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : became reoriented 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 initiated the holding pattern entry. I alerted him that we had not crossed the fix. As he was interrupting the automatic flight control system to override the autoplt's turn the autoplt disconnected. The aircraft descended approximately 1000 ft before the captain recovered. Confusion over when to start the holding entry resulted in part, because the captain's data is displayed from the flight management system while the copilot display is VOR based only. The captain's display indicated station passage while my side did not. Other contributing factors. 1) when the autoplt disconnected there is only a momentary light on the annunciator panel with no warning tone or master caution light. 2) when the afcs is interrupted the command bars on the ADI stay on the miniature aircraft even if altitude hold is selected therefore they don't indicate variations in selected altitude. 3) copilot's altimeter is separate from the air data computer and indicates higher than the captain's altimeter at the same altimeter setting. Although altitude correction was initiated when the altitude alerter chimed at 100 ft low the aircraft lost a considerable amount of altitude in the confusion. Crew coordination should have resulted in confirmation of station passage prior to initiating the turn. This would have compensated for the difference in the RNAV (FMS) indications and the VOR.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION.

Narrative: THE CAPT INITIATED THE HOLDING PATTERN ENTRY. I ALERTED HIM THAT WE HAD NOT CROSSED THE FIX. AS HE WAS INTERRUPTING THE AUTOMATIC FLT CTL SYS TO OVERRIDE THE AUTOPLT'S TURN THE AUTOPLT DISCONNECTED. THE ACFT DSNDED APPROX 1000 FT BEFORE THE CAPT RECOVERED. CONFUSION OVER WHEN TO START THE HOLDING ENTRY RESULTED IN PART, BECAUSE THE CAPT'S DATA IS DISPLAYED FROM THE FLT MGMNT SYS WHILE THE COPLT DISPLAY IS VOR BASED ONLY. THE CAPT'S DISPLAY INDICATED STATION PASSAGE WHILE MY SIDE DID NOT. OTHER CONTRIBUTING FACTORS. 1) WHEN THE AUTOPLT DISCONNECTED THERE IS ONLY A MOMENTARY LIGHT ON THE ANNUNCIATOR PANEL WITH NO WARNING TONE OR MASTER CAUTION LIGHT. 2) WHEN THE AFCS IS INTERRUPTED THE COMMAND BARS ON THE ADI STAY ON THE MINIATURE ACFT EVEN IF ALT HOLD IS SELECTED THEREFORE THEY DON'T INDICATE VARIATIONS IN SELECTED ALT. 3) COPLT'S ALTIMETER IS SEPARATE FROM THE AIR DATA COMPUTER AND INDICATES HIGHER THAN THE CAPT'S ALTIMETER AT THE SAME ALTIMETER SETTING. ALTHOUGH ALT CORRECTION WAS INITIATED WHEN THE ALT ALERTER CHIMED AT 100 FT LOW THE ACFT LOST A CONSIDERABLE AMOUNT OF ALT IN THE CONFUSION. CREW COORD SHOULD HAVE RESULTED IN CONFIRMATION OF STATION PASSAGE PRIOR TO INITIATING THE TURN. THIS WOULD HAVE COMPENSATED FOR THE DIFFERENCE IN THE RNAV (FMS) INDICATIONS AND THE VOR.

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.