Moonshot: The Inside Story of Mankind's Greatest Adventure by Dan Parry

yellow warning light along with an intermittent alarm.
Armstrong [to Houston]: 'Program alarm.'
Mission Control: 'It's looking good to us. Over.'
Armstrong [to Houston]: 'It's a 1202.'
Aldrin: '1202.'
Armstrong [to Aldrin]: 'What is it?'
On the ground, Bales – who had been preoccupied with the navigation error – now needed to work out how much trouble the computer was in. He quickly talked over the internal radio loop to Jack Garman, his backroom specialist, who told him that 1202 was a reference to 'executive overflow'. The computer was struggling to complete some of its tasks, just as had happened prior to the 1201 alarm during training. To Neil and Buzz, however, the alarm code was unfamiliar, and Armstrong was forced to break his concentration and pay close attention to the spacecraft's systems. Without knowing what the problem was it was impossible to know how much danger they were in.

This time, unlike the training session, Bales looked at whether there were any actual problems with the guidance and navigation data. The telemetry suggested that everything seemed to be working well. Since the computer hadn't crashed altogether but had simply returned to the top of its list of tasks, Bales decided the alarm could be ignored. The computer could still function – as long as it wasn't pushed any further. If it began to trigger successive alarms he knew they would have to abort. Armstrong didn't know if they were at that point already, and Buzz later said that 'hearts shot up into throats while we waited to learn what would happen'. 32
Bales told Kranz that the mission could continue, and Kranz instructed Duke to give the go-ahead to the crew.
Mission Control: 'Roger. We're go on that alarm.'
With Eagle now down to 27,000 feet, less than 30 seconds later the alarm rang out again. This time Buzz realised it sounded whenever he asked the computer how far they were from the landing site.
Aldrin: 'Same alarm, and it appears to come up when we have a 16-68 up.'
Mission Control: 'Roger. Copy.'
Armstrong [to Aldrin]: 'Were we – were – was it [their delta- H] coming down?'
Aldrin: 'Yes, it is coming down beautifully.'
Mission Control: ' Eagle , Houston. We'll monitor your delta-H.'
The spacecraft was flying at 800mph, at an altitude of three and a half miles. Now that Houston was easing its workload, the computer was free to begin the next phase of the landing sequence. At six minutes and 25 seconds into the burn the digital autopilot slowed the engine. Still flying horizontally, feet first, Neil would soon have to slowly pitch up so that Eagle assumed more of an upright position.

At home in Houston, Janet Armstrong and 12-year-old Ricky sat on the floor listening to the television while studying lunar maps and diagrams. Thinking of Neil standing up like a trolleybus driver as he flew towards the surface, Janet excitedly called out, 'Come on, come on, trolley!' 33
In Mission Control, Jay Greene – his quickfire Brooklyn accent cutting across the radio loop – told Kranz that the trajectory looked good. At 5,000 feet above the ground Neil got ready to take over from the digital autopilot, and with less than four minutes remaining he briefly tested the hand controller. Satisfied with its response, he focused on the view ahead. The surface was filling more and more of his window as Eagle approached a vertical position, the Sun now directly behind them. At 4,000 feet Kranz polled the controllers ahead of the landing.
Mission Control: ' Eagle , Houston. You're go for landing. Over.'
Aldrin: 'Roger. Understand. Go for landing; 3,000 feet.'
Mission Control: 'Copy.'
Aldrin: 'Program alarm – 1201.'

Alarms sounded a total of five times during the descent. They did not recur frequently enough to prompt an abort but they were a major distraction for Neil. The computer was bringing them down on a specific trajectory and would not swerve from its course despite the fact it couldn't tell whether it was taking them towards rocks or a