Flight crew of air carrier light transport aircraft inadvertently descended below clearance and MEA ...

Attributes
ACN	219276
Time
Date	199208
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mtj
State Reference	CO
Altitude	msl bound lower : 12000 msl bound upper : 12400
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute airway : zdv
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 155 flight time total : 13400 flight time type : 840
ASRS Report	219276
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	flight crew : exited adverse environment flight crew : became reoriented flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During descent for approach into mtj the aircraft descended 400 ft below the MEA of 12400 to 12000. The error was pointed out by the controller. The flight had been climbing out from mtj en route den when a malfunction in the pressure controller caused the cabin to start to climb above 10000. Since MEA's further along the route precluded unpressurized flight below 10000 ft it was decided to return to mtj. Clearance was received to return and the crew donned oxygen masks. The captain took control of the aircraft while the first officer donned his mask. The aircraft was cleared for an approach into mtj upon being established on V26 and to report descending through 13000. The first officer had some trouble with his mask straps and the captain missed the 13000 call. The captain thought the MEA was 12000 and descended to that altitude. Upon being informed of the error by center, an immediate climb was performed to 12400. The captain thought the MEA was 12000 as he had shot the approach into mtj but from a different airway where the MEA was 12000, and misread the chart during the approach briefing. Contributing factors were the distrs of company calls, passenger briefing, and the difficulties encountered by the first officer with his face mask straps. Also, the crew had flown 5 legs already for a total of 5 hours 18 mins and had been on duty since AM31. Although fatigue had not reached a high level, it was at least a factor to consider. In retrospect, this was a chilling reminder of the need to constantly monitor the MSA and not allow extraneous factors to distract the crew.

Original NASA ASRS Text

Title: FLC OF ACR LTT ACFT INADVERTENTLY DSNDED BELOW CLRNC AND MEA ALT LIMIT DURING DSCNT FOR AN EMER RETURN TO THE ARPT.

Narrative: DURING DSCNT FOR APCH INTO MTJ THE ACFT DSNDED 400 FT BELOW THE MEA OF 12400 TO 12000. THE ERROR WAS POINTED OUT BY THE CTLR. THE FLT HAD BEEN CLBING OUT FROM MTJ ENRTE DEN WHEN A MALFUNCTION IN THE PRESSURE CTLR CAUSED THE CABIN TO START TO CLB ABOVE 10000. SINCE MEA'S FURTHER ALONG THE RTE PRECLUDED UNPRESSURIZED FLT BELOW 10000 FT IT WAS DECIDED TO RETURN TO MTJ. CLRNC WAS RECEIVED TO RETURN AND THE CREW DONNED OXYGEN MASKS. THE CAPT TOOK CTL OF THE ACFT WHILE THE FO DONNED HIS MASK. THE ACFT WAS CLRED FOR AN APCH INTO MTJ UPON BEING ESTABLISHED ON V26 AND TO RPT DSNDING THROUGH 13000. THE FO HAD SOME TROUBLE WITH HIS MASK STRAPS AND THE CAPT MISSED THE 13000 CALL. THE CAPT THOUGHT THE MEA WAS 12000 AND DSNDED TO THAT ALT. UPON BEING INFORMED OF THE ERROR BY CTR, AN IMMEDIATE CLB WAS PERFORMED TO 12400. THE CAPT THOUGHT THE MEA WAS 12000 AS HE HAD SHOT THE APCH INTO MTJ BUT FROM A DIFFERENT AIRWAY WHERE THE MEA WAS 12000, AND MISREAD THE CHART DURING THE APCH BRIEFING. CONTRIBUTING FACTORS WERE THE DISTRS OF COMPANY CALLS, PAX BRIEFING, AND THE DIFFICULTIES ENCOUNTERED BY THE FO WITH HIS FACE MASK STRAPS. ALSO, THE CREW HAD FLOWN 5 LEGS ALREADY FOR A TOTAL OF 5 HRS 18 MINS AND HAD BEEN ON DUTY SINCE AM31. ALTHOUGH FATIGUE HAD NOT REACHED A HIGH LEVEL, IT WAS AT LEAST A FACTOR TO CONSIDER. IN RETROSPECT, THIS WAS A CHILLING REMINDER OF THE NEED TO CONSTANTLY MONITOR THE MSA AND NOT ALLOW EXTRANEOUS FACTORS TO DISTRACT THE CREW.

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.

Flight crew of air carrier light transport aircraft inadvertently descended below clearance and MEA altitude limit during descent for an emergency return to the airport.