After taking off from Anchorage, the flight was instructed by air traffic control (ATC) to turn to a heading of 220 degrees. Approximately 90 seconds later, ATC directed the flight to "proceed direct Bethel when able". Upon arriving over Bethel, Alaska, flight 007 entered the northernmost of five 50-mile (80 km) wide airways, known as the NOPAC (North Pacific) routes, that bridge the Alaskan and Japanese coasts. KAL 007's particular airway, R-20 (Romeo Two Zero), passes just 17.5 miles (28.2 km) from what was then Soviet airspace off the coast of the Kamchatka Peninsula.
The autopilot system used at the time had four basic control modes: HEADING, VOR/LOC, ILS, and INS. The HEADING mode maintained a constant magnetic course selected by the pilot. The VOR/LOC mode maintained the plane on a specific course, transmitted from a VOR (VHF omnidirectional range, a type of short-range radio signal transmitted from ground beacons) or Localizer (LOC) beacon selected by the pilot. The ILS (instrument landing system) mode caused the plane to track both vertical and lateral course beacons, which led to a specific runway selected by the pilot. The INS (inertial navigation system) mode maintained the plane on lateral course lines between selected flight plan waypoints programmed into the INS computer.
When the INS navigation systems were properly programmed with the filed flight plan waypoints, the pilot could turn the autopilot mode selector switch to the INS position and the plane would then automatically track the programmed INS course line, provided the plane was headed in the proper direction and within 7.5 nautical miles (13.9 km) of that course line. If, however, the plane was more than 7.5 miles (12.1 km) from the flight-planned course line when the pilot turned the autopilot mode selector from HEADING to INS, the plane would continue to track the heading selected in HEADING mode as long as the actual position of the plane was more than 7.5 miles (12.1 km) from the programmed INS course line. The autopilot computer software commanded the INS mode to remain in the "armed" condition until the plane had moved to a position less than 7.5 miles (12.1 km) from the desired course line. Once that happened, the INS mode would change from "armed" to "capture" and the plane would track the flight-planned course from then on.
The HEADING mode of the autopilot would normally be engaged sometime after takeoff to comply with vectors from ATC, and then after receiving appropriate ATC clearance, to guide the plane to intercept the desired INS course line.
The Anchorage VOR beacon was not operational because of maintenance. The crew received a NOTAM (Notice to Airmen) of this fact, which was not seen as a problem, as the captain could still check his position at the next VORTAC beacon at Bethel, 346 miles (557 km) away. The aircraft was required to maintain the assigned heading of 220 degrees, until it could receive the signals from Bethel, then it could fly direct to Bethel, as instructed by ATC, by centering the VOR "to" course deviation indicator (CDI) and then engaging the auto pilot in the VOR/LOC mode. Then, when over the Bethel beacon, the flight could start using INS mode to follow the waypoints that make up route Romeo-20 around the coast of the U.S.S.R. to Seoul. The INS mode was necessary for this route, since after Bethel the plane would be mostly out of range from VOR stations.
At about 10 minutes after take-off, KAL 007, flying on a heading of 245 degrees, began to deviate to the right (north) of its assigned route to Bethel, and continued to fly on this constant heading for the next five and a half hours.
International Civil Aviation Organization (ICAO) simulation and analysis of the flight data recorder determined that this deviation was probably caused by the aircraft's autopilot system operating in HEADING mode, after the point that it should have been switched to the INS mode. According to the ICAO, the autopilot was not operating in the INS mode either because the crew did not switch the autopilot to the INS mode (shortly after Cairn Mountain), or they did select the INS mode, but the computer did not transition from INERTIAL NAVIGATION ARMED to INS mode because the aircraft had already deviated off track by more than the 7.5 nautical miles (13.9 km) tolerance permitted by the inertial navigation computer. Whatever the reason, the autopilot remained in the HEADING mode, and the problem was not detected by the crew.
At 28 minutes after takeoff, civilian radar at Kenai Peninsula on the eastern shore of Cook Inlet and with radar coverage 175 miles (282 km) west of Anchorage, tracked KAL 007 5.6 miles (9.0 km) north of where it should have been.
When KAL 007 did not reach Bethel at 50 minutes after takeoff, a military radar at King Salmon, Alaska, tracked KAL 007 at 12.6 nautical miles (23.3 km) north of where it should have been. There is no evidence to indicate that civil air traffic controllers or military radar personnel at Elmendorf Air Force Base (who were in a position to receive the King Salmon radar output) were aware of KAL 007's deviation in real-time, and therefore able to warn the aircraft. It had exceeded its expected maximum deviation sixfold, 2 nautical miles (3.7 km) of error being the maximum expected drift from course if the inertial navigation system was activated.
KAL 007's divergence prevented the aircraft from transmitting its position via shorter range very high frequency radio (VHF). It therefore requested KAL 015, also en route to Seoul, to relay reports to air traffic control on its behalf. KAL 007 requested KAL 015 to relay its position three times. At 14:43 UTC, KAL 007 directly transmitted a change of estimated time of arrival for its next waypoint, NEEVA, to the international flight service station at Anchorage, but it did so over the longer range high frequency radio (HF) rather than VHF. HF transmissions are able to carry a longer distance than VHF, but are vulnerable to electromagnetic interference and static; VHF is clearer with less interference, and preferred by flight crews. The inability to establish direct radio communications to be able to transmit their position directly did not alert the pilots of KAL 007 of their ever-increasing divergence and was not considered unusual by air traffic controllers. Halfway between Bethel and waypoint NABIE, KAL 007 passed through the southern portion of the North American Aerospace Defense Command buffer zone. This zone is north of Romeo 20 and off-limits to civilian aircraft.
Some time after leaving American territorial waters, KAL Flight 007 crossed the International Date Line, where the local date shifted from August 31, 1983, to September 1, 1983.
KAL 007 continued its journey, ever increasing its deviation60 nautical miles (110 km) off course at waypoint NABIE, 100 nautical miles (190 km) off course at waypoint NUKKS, and 160 nautical miles (300 km) off course at waypoint NEEVAuntil it reached the Kamchatka Peninsula.