Audio transcripts released by the US FAA have detailed air traffic controllers' bid to contact Northwest flight NW188 after the Airbus A320 failed to respond to calls and far overshot Minneapolis, its destination, last month.
The transcripts from 21 October show that NW188 from San Diego passed through Denver en route centre's radar sector 30 and sector 28 without problem, and acknowledged a change of frequency to 132.17MHz at 17:56MST.
But three subsequent frequency-change instructions in the space of 20min - from Denver radar sectors 18, 08 and 09 - went unanswered. After a radio check, the sector 09 controller asked Minneapolis en route centre whether the aircraft had "come over", and was told it had not.
"I'll go find him," the Denver controller assured. But attempts to raise NW188 were unsuccessful and some 45min after its last contact, the Minneapolis R29 controller informed a colleague, at R19, that the flight was "actually nordo" - meaning 'no radio'.
R19 then asked another Northwest flight, NW196, to try to reach the pilots, and also contacted other controllers at R11, R15 and R16.
With the aircraft still unresponsive more than 30min later, and 50 miles beyond Minneapolis, the R29 controller suggested that the centre "try another pilot, see if he can get him" by using the last Denver frequency, 126.32MHz.
The R13 controller asked a third Northwest flight, NW1553, to call the wayward aircraft on this frequency and, if successful, tell the pilots to contact Minneapolis.
Shortly afterwards the R16 controller asked another flight, NW1510, to do the same. But almost simultaneously, NW188 re-established contact with R13, and R16 stated: "They got him. I just heard they got him."
NW188, having been silent for 1hr 17min, then told the R13 controller: "We got distracted and we've overflown Minneapolis, we are overhead Eau Claire and would like to make a 180 and do arrival from Eau Claire."
R13 told the crew that it needed to verify that the cockpit was secure. "It is secure, we got distracted," responded NW188, the pilots adding that they "never heard a call".
Control of the flight passed to R16 who, after a fuel check, asked: "Do you have time to give a brief explanation on what happened?"
The pilot replied: "Just cockpit distractions, that's all I can say."
Despite the minimal explanation, the R16 controller tried to obtain more detail a few minutes later: "Northwest 188 is there any way you can elaborate on the distraction?"
"We're just dealing with some company issues here," the crew said. "And that's all, that's all I can tell you right now at this time."