Problems with the Sanders display unit [see chapter 15-8] in the firing room forced a postponement of the flight readiness test on 15 November. The second attempt on the 19th proved successful. The presence of a crew led to some alterations in the launch procedures. The commander could call a "hold" if he felt it necessary, or he could initiate an inflight abort. Weather restrictions for the launch were supplemented to meet the danger of impacting on land after a pad abort. The presence of a thunderstorm cell within 20 miles of the pad could force crew egress, and under no circumstances could a launch take place during or through a thunderstorm. These contingencies were the province of the flight director (who took control of the flight once the vehicle had cleared the tower of the mobile launcher), the launch operations manager, and the test supervisor.64
The countdown demonstration test for AS-503 began early on 5 December. The spacecraft slipped approximately 14 hours behind schedule because of problems in the astronaut communications and cryogenic systems. On 8 December the wet test progressed to T-9 hours when a problem in a data transmission system caused several hours delay. Later in the day an error in the memory of a digital events evaluator and a malfunction in a helium regulator terminated operations. The launch team resumed the following morning after the problems were resolved. A defective heat exchanger in the third stage's ground support equipment halted operations at T-2.5 hours. Once again the test conductor recycled the test clock to begin at T-9 hours the morning of the 10th. After completing the test by mid-afternoon, the launch team concluded the demonstration test with a dry run the following day. Problems with the astronaut communication system and ground support equipment were grim reminders of the 204 disaster.65
The launch countdown for Apollo 8 began at 7:00 p.m. on 15 December and headed for a launch on the 21st. The following day, a three-hour physical examination found the crew in good health. Both the men and the machine appeared ready.66