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November Flite Facts Page 13. DUAL VOR'S - UTILIZE TWA operating policy prescribes maximum cross checking of the dual VOR capability. This includes aural identification of the station for both VOR and DME and warning flag display. Good habits in this regard are important. There have been cases, according to FAA, of internal airborne equipment failure, without actuating warning flag. This resulted in erroneous guidance information which was not readily detectable by the pilot. The FAA issued advisory circular No. AC 43-1 on this subject. It is reprinted in part below. "There have been several instances where a VOR/ILS navigation receiver failed and provided inaccurate guidance information, but did not show a flag alarm. In these particular cases, investigation revealed that if one channel failed (either reference, variable phase, 90 or 150 cps) the flag would not appear as required in the flag specifications outlined in Technical Standard Orders C40a, C34b and C36b. It was determined that the installed pictorial deviation indicator's flag alarm movement had considerably greater sensitivity (needing less current to remain concealed) than that amount to which the receivers were adjusted, and the associated aircraft interwiring and loading resistors did not take this into account. Similar mismatching in course deviation indicating circuits will also give erroneous guidance information. These types of erroneous indications are avoided by proper equipment matching." [[image]] - Equipment General - FIRE EXTINGUISHER PRESSURE VS. TEMPERATURE The HRD fire extinguisher containers used on TWA aircraft contain a mixture of monobromotrifluoromethane (commonly called tri-bromo) and nitrogen. The tri-bromo is a very effective extinguishing agent, whereas the nitrogen as a propellant assures rapid discharge. Various sizes of containers are used by TWA for different aircraft. The pressure of the charge in an HRD container varies considerably with temperature. This variation is slightly different for each size container because of the different tri-bromo/nitrogen weight ratios used in the various sizes of containers. To determine what the correct pressure is for a given temperature it is necessary to consult the temperature correction charts in the Maintenance Manual. It must be kept in mind that the temperature of the container may vary considerably from ambient ground temperature if the containers have been cold soaked in a long, high altitude flight. Therefore, if the container feels colder than ambient, before replacing it for a low pressure condition, the container skin temperature is checked with a surface thermometer. When this thermometer is placed with its back (black) side against the container, it reads container (and not ambient) temperature. The container temperature is then used to find required container pressure. Maintenance Manuals list the temperature/pressure requirements. WEIGHT MEASURING SYSTEM The DC-9's are scheduled for maintenance
