BE1900 flight crew reports detecting symptoms of hypoxia while cruising at FL190. The cabin altitude...

Narrative:

The first officer was the pilot flying on this leg and and just prior to reaching the lar VOR we both noticed symptoms of hypoxia. The first officer noticed the cabin altimeter was showing somewhere between 12 and 13 thousand feet; maybe a little higher. There was no associated cabin attendant altitude hi annunciator. I checked the annunciators with a press to test and the cabin attendant altitude hi tested normally. After a few moments of disbelief we elected to don our oxygen masks and requested a lower altitude; which was granted. I ran the cabin decompression emergency checklist. I elected not to deploy the cabin oxygen masks since we were descending and cabin altitude was now indicated below 12;000 feet. Crew and ATC communications were difficult due to the oxygen masks. Once we reached 10;000 we removed our masks and landed normally. We did not declare an emergency since we were given a descent. It should be noted that the left environmental system was MEL'ed under 21-14 and the cabin was quite cold which we assumed was a result of the MEL. The cabin attendant altitude hi is supposed to be our safety net and it did not illuminate. Had this been working we would have discovered this earlier in the flight. I don't feel that we could have done anything differently as a crew.

Original NASA ASRS Text

Title: BE1900 flight crew reports detecting symptoms of hypoxia while cruising at FL190. The cabin altitude is noted between 12- and 13;000 feet and oxygen masks are doned and a descent is initiated. There was no associated CAB ALT HI annunciation although the light tested normally.

Narrative: The First Officer was the pilot flying on this leg and and just prior to reaching the LAR VOR we both noticed symptoms of hypoxia. The First Officer noticed the cabin altimeter was showing somewhere between 12 and 13 thousand feet; maybe a little higher. There was no associated CAB ALT HI annunciator. I checked the annunciators with a press to test and the CAB ALT HI tested normally. After a few moments of disbelief we elected to don our oxygen masks and requested a lower altitude; which was granted. I ran the Cabin Decompression Emergency Checklist. I elected not to deploy the cabin oxygen masks since we were descending and cabin altitude was now indicated below 12;000 feet. Crew and ATC communications were difficult due to the oxygen masks. Once we reached 10;000 we removed our masks and landed normally. We did not declare an emergency since we were given a descent. It should be noted that the left environmental system was MEL'ed under 21-14 and the cabin was quite cold which we assumed was a result of the MEL. The CAB ALT HI is supposed to be our safety net and it did not illuminate. Had this been working we would have discovered this earlier in the flight. I don't feel that we could have done anything differently as a crew.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1054124
Time
Date	201212
Local Time Of Day	1201-1800
Place
Locale Reference	ZDV.ARTCC
State Reference	CO
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Make Model Name	Beech 1900
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Pressurization System
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Commercial
Events
Anomaly	Aircraft Equipment Problem Critical

BE1900 flight crew reports detecting symptoms of hypoxia while cruising at FL190. The cabin altitude is noted between 12- and 13;000 feet and oxygen masks are doned and a descent is initiated. There was no associated cabin attendant altitude hi annunciation although the light tested normally.