Despite all the trials KSC had gone through with AS-501 by September, more were ahead. On 31 August the launch operations office issued a new schedule with the countdown demonstration test to begin 20 September. In less than a week the schedule was broken. When Boeing had to replace the hydraulic engine actuators on the first stage, Petrone's office rescheduled the test for 25 September. A major milestone, the space vehicle malfunction overall test, was scrubbed on the 12th because of rain and high winds. The test team concluded the exercise the following day, but lightning slowed down operations on the 14th. For later flights the sequence would be flight readiness test, countdown demonstration test, countdown and launch. For the first flight of the Saturn V, however, the test directors wanted to have the flight readiness test as close to the launch date as possible and scheduled it after the demonstration test. KSC officials were not at all sure how well the new launch complex would perform. Events would justify their concern.27
The six-day countdown test started on the evening of 27 September. By 2 October the launch team was two days behind schedule. Following a hold, the test went smoothly from T-18 to T-13 hours, when computer problems forced another delay. The count reached T-45 minutes on 4 October when a computer, monitoring the propellant loading operation, failed. As a result 1,900,000 liters of kerosene and liquid oxygen had to be removed from the S-IC stage. The count, set back to T-13 hours, was resumed on 9 October. More computer problems and a faulty regulator on the helium gas system marred operations that day. By the time the count reached T-5 hours, the launch team was exhausted. Petrone called a two-day recess. Shortly after the test resumed on 11 October, a problem appeared with a battery heater on the S-II stage. As the battery could not be repaired or replaced quickly, another day's work was cancelled. KSC finally completed the test on 13 October, after 17 frustrating days.28
As Paul Donnelly later noted: "In spite of the many problems encountered in the test, the crew had received an education that money couldn't buy."29 The launch date for Apollo 4 was postponed, pending the outcome of the test. After it was completed, few at KSC seriously believed that 501 could be launched on the new date of 7 November. Phillips acknowledged that "this is a target date. We are in a very complex learning process and we are going to take all the time we need on this first launch."30 The growing concern of higher NASA management expressed itself at the flight readiness review on 19 October. The purpose of this meeting was to assess the readiness of the overall mission in general and the S-II in particular. Because it was unmanned, Apollo 4 was cleared for launch assuming the satisfactory completion of the remaining tests and modifications.31