On June 9, 1995, the cruise ship Royal Majesty left St. George’s, Bermuda, for Boston with 1,509 people on board. Before departure the navigator tested the equipment and found it in “perfect” operating condition. He set the autopilot to steer by the ship’s GPS.
About an hour later, the cable from the GPS antenna came loose at its connector. The receiver did what it was configured to do when satellite data stopped: it switched to dead reckoning, estimating the ship’s position from its speed and heading. It announced the change with a series of chirps lasting one second in all, and with the small letters “DR” and “SOL” on its screen. The receiver sat in the chart room, away from the main console.
The autopilot couldn’t tell the difference. It kept steering toward the planned track using positions that no longer accounted for wind or current. An east-northeasterly wind and sea pushed the ship steadily west-southwest.
The officers had seen “DR” and “SOL” before. The GPS sometimes glitched for a few minutes, making the radar map jump, a problem the crew called “chopping,” and the letters appeared with it. On this trip they stayed.
The ship also carried a second, independent position receiver, a Loran-C. The second officer, who had the watch in the final hours, testified that he treated it as a backup and that it was not his practice to use it to verify the GPS.
On the evening of June 10, approaching the Boston traffic lanes, the chief officer saw a radar target about where he expected the entrance buoy and concluded that was what it was. Later, lookouts reported a yellow light, then several red lights, off the port side. The second officer acknowledged each report and took no action. The captain came to the bridge, saw the display showing the ship within 200 meters of its intended track, and left. A lookout reported blue and white water dead ahead.
At about 10:25 p.m., the Royal Majesty ran aground on Rose and Crown Shoal near Nantucket, about 17 miles from where its officers believed it was. Nobody was hurt. Damage and lost revenue came to about $7 million.
The NTSB found that the officers had failed to notice the ship’s errant course for more than 34 hours. It named as probable cause “the watch officers’ overreliance on the automated features of the integrated bridge system,” along with gaps in training and in the system’s design.
At the site of the grounding, the report noted, the Loran-C was showing the ship’s correct position.