OPERATING LIMITATIONS

The primary operating limitation connected with EC-47 operations in SEA revolved around the mutual desire of MACV and the TEWS to provide maximum time for over- target coverage, coupled with the necessity to comply withe the regulations stipulating a 100 foot-per-minute rate of climb in the event of loss of an engine on takeoff. MACV desired seven-hour sorties on all ARDF missions. With the EC-47Q and its more powerfull engines, this did not constitute a problem, regardless of whether the aircraft was configured CC or CCZ. With the EC-47N/P in the straight Combat Cross configuration ("X" and "Y" consoles only) it too, constituted no problem.

The difficulties arose with the EC-47N/P in the Combat Cross Zulu configuration, with its two extra "Z" consoles, associated equipment, and additional personnel. The seven-hour requirement could not be met, since the fuel needed for the mission would place the aircraft far under the 100 foot-per-minute rate of climb requirement. The takeoff weights remained the same for long or short missions, but the additional weight in the CCZ EC-47N/Ps forced a reduction in allowable fuel, in order to meet the weight requirements. Depending upon temperature, humidity and altitude (all of which affect engine performance), 27,000 pounds or a little less, was the maximum allowable gross takeoff weight. Approximately 200 fewer gallons of fuel (roughly 1,200 pounds) could be carried in the EC-47N/P CCZ aircraft--a loss which reduced their total sortie time of five hours.

Cruise control procedures whereunder pilots reduced power as fuel was consumed were instituted. By so doing, they enabled the aircraft to maintain proper airspeed while using less gasoline. The net result was that as aircraft weight was reduced, less fuel was consumed, and aircraft sortie time could be extended to the maximum.

It appeared to be a never-ending battle. As more equipment was added, new ways had to be found to reduce other weight. Leaflet drops, as a cover for operations, were discontinued to reduce weight (although the door was left open for their possible resumption). For the same reason, the use of a flight engineer on most missions was also discontinued. The "Q" (jamming) configuration was removed to reduced weight further.

But for every step forward, it seemed that there was another step back. On 22 September 1969, Mod 545 installation of polyurethane foam in EC-47 fuel tanks was started. The purpose of the foam was to reduce the hazard of fuel fires or explosions, but the modification added 210 pounds to the basic weight of the aircraft and reduced fuel capacity by 4.5 percent -- 36 gallons. At 90 gallons- per-hour fuel consumption, this reduced sortie time by about 24 minutes.

Much effort and paperwork went into a request for a waiver to reduce the 100 feet-per-minute restriction to 75 fpm on single engine. Much of the controversy - and it turned out to be a controversy--hinged on the accuracy or inaccuracy of the C-47-1 performance charts, which differed from some flight test data. The issue involved 7AF, the 460th TRW, Hq PACAF, WRAMA, and the Air Force Flight Test Center for over a year, without being resolved. As of this writing, it had still not been resolved; however, a mid-August WRAMA message said, in part, "New performance charts will be issued to replace T.O. 1c-47-1SS-7, dated 17 Feb. 70. Charts will be available approximately 10 Sep 70."

Several other restrictions influenced Combat Cross operations, including friendly artillery areas, Arc Light strikes, congested flight areas, ans susceptibility to enemy fire. The altitude restrictions imposed upon the EC-47' depended upon the ground threat in the area being worked. Generally, over South Vietnam, 3,500 feet was minimum altitude. Over Laos, where the threat was know, 4,500 feet AGL (above ground level) was the rule, and, when overflights of Cambodia, 7,000 feet was the initial working altitude. In theory, the higher altitude--giving a longer slant range from aircraft to target radio--should have made the fixes less accurate, but in practice this does not seem to have been the case. In the opinion of the 460th TRW DCOE, 7,000-foot AGL fixes were apparently as accurate as those taken in South Vietnam; therefore, consideration was given to make the operating altitude 7,000 feet above ground level in all areas. Obviously, though, in some areas of northern South Vietnam and in Laos, where the highest elevations ranged up to 10,000 feet, this would not be very feasible.