Compact instruments, similar in appearance to common personal pagers, have been proposed for warning aircraft crewmembers that cabin air pressure has decreased to a potentially dangerous level. An instrument of this type, called a "personal cabin pressure monitor and warning system" (PCPMWS), implements a warning protocol consistent with Federal Aviation Administration (FAA) requirements for commercial flight crews to (1) use supplemental oxygen after a 30-minute exposure to a cabin pressure altitude between 10,000 and 12,000 ft (about 3,050 and 3,660 m), or (2) immediately when the cabin pressure altitude exceeds 12,000 ft. The PCPMWS would provide both 10,000- and 12,000-ft warnings. The elapsed time between these two warning altitudes could also serve as an indication of the rate of decompression, and thus of the urgency of the situation.

A PCPMWS is a state-of-the-art system which incorporates recent advances in sensors, low-power electronic circuitry, and high-density packaging of electronic circuitry. A production-model would be small, robust, and highly accurate. A PCPMWS contains a battery, an internal temperature-compensated pressure monitor, a microprocessor, an audio alarm, a vibrating alarm, and visual displays that would include a flashing light-emitting diode and a digital display or bar graph that would indicate the current cabin pressure altitude. The display would also serve as an indicator of the condition of the battery and functioning of the system when a momentary "TEST" button was pressed. Because a PCPMWS is a safety device, the user must depress the power switch for several seconds in order to power down the unit.

If a PCPMWS senses a cabin pressure altitude above the 10,000-ft trigger point, the audio, vibrating, and visual alarms will temporarily activate and start a 30-minute timer. If a pressure altitude between 10,000 and 12,000 ft is detected for 30 minutes or more, or immediately upon detection of a pressure altitude of 12,000 ft or more, all alarms will activate. A "TEMPORARY ALARM RESET" button will silence the alarms for 5 minutes. If the pressure condition causing the alarm is still present after the 5-minute period, the alarms will again sound. The user can configure the unit not to repeat the alarms, if so desired. Since the supplemental oxygen rules for general-aviation pilots are slightly different than for commercial operators, the unit will automatically select the applicable pressure altitude trigger points when the user selects the type of flight operation intended.

The PCPMWS is useful for both pressurized and nonpressurized aircraft operations. The device would serve as a reminder to the crew when supplemental oxygen is required for nonpressurized aircraft, and serve as a warning when the required safe cabin pressure altitude has been compromised in a pressurized aircraft. The main advantages of a PCPMWS are its portability and independence of other aircraft systems. Since the PCPMWS architecture is microprocessor-based, pressure altitude, temperature, and local pressure indications can be displayed in any convenient units of measure. Thus, it could serve as a supplemental or emergency pressure altimeter or pressure monitor for a balloon, glider, or other nonpressurized aircraft. The microprocessor could also calculate the rate of change of altitude, so that the PCPMWS could also serve as a supplemental rate-of-climb indicator.

This work was done by Jan A. Zysko of Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at under the Test and Measurement category.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

the Technology Programs and Commercialization Office
Kennedy Space Center
(321) 867-6373.

Refer to KSC-12168.