ECHO Air Design Testing for a Boeing 737

The ECHO Air system is designed to eliminate or significantly reduce aircraft envelope condensation which can promote undesirable and potentially hazardous effects such as 'rain in the plane', microbial growth, electrical system deterioration, fuselage corrosion, and dead weight accumulation. By pressurizing the envelope with a portion of the dry ventilation air prior to its entry into the cabin, the system provides a dynamic barrier that prevents cabin air infiltration into the envelope through thermal-gradient induced "stack" pressures. Coincidentally, passing ventilation air through the envelope improves cabin air quality through absorption and filtering of such contaminants as ozone, oil aerosols and combustion VOCs without the high pressure drops associated with standard filtration systems.

Test findings described in this report for an older B 737-200 clearly show that its liner panel joint tightness ensures an envelope pressurization that will prevent cabin air infiltration throughout the cabin under the worst case cold soak condition using only a fraction of the cabin ventilation air. Studies of injector placement indicate a facile and economic installation of the ventilation air injectors for this aircraft. Air injection positions and rates can readily be modified for other aircraft models using ground air flow/ pressure measurements followed by in-flight tests of stack pressure and temperature to confirm optimal placement.

Measurements were also made of volatile organic compounds in the envelope and cabin ventilation air. Envelope air had a high proportion of petroleum VOCs emanating from its anti-corrosion treatment as well as a high quantity of microbial VOCs. The gasper ventilation air contained a high proportion of combustion VOCs. It is postulated that these VOCs were previously absorbed on oil deposits in the gasper ducts during incidents of ground exhaust ingestion rather than from ingestion of engine exhaust during the test flight.

The inclusion of envelope dampered outlets to the cabin exhaust air ducts and control of envelope injection rates permit depressurization as well as pressurization relative to the cabin. This capability can be used to purge the envelope of air contaminants at appropriate stages of the flight cycle, to improve cabin smoke venting capability in the event of a fire, and to permit the safe injection of fire suppressant into the envelope without exposing the passengers to any associated hazardous gases.

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