39 years ago on the 4th of September 1971, Alaska Airlines Flight 1866 crashed on approach to Juneau, Alaska.
The Boeing 727, carrying 104 passengers and 7 crew members, flew into the Chilkat Mountain range. There were no survivors.
Aircraft Accident Report, Alaska Airlines, Inc. Boeing 727, N2969G
The flight had been cleared for a Localizer Directional Aid (LDA) approach to Runway 8 and had reported passing the final approach fix inbound to the airport. This intersection is located 10.2 nautical miles west of the airport.
No further communications were heard from the flight.
Search and rescue found the wreckage 18.5 NM west of the airport. They had crashed into the slope of a canyon in the Chilkat Mountains. The wreckage was found around the 2,500 foot level, in “near-alignment with the Juneau localizer course”.
(See the comments below for an identification of this photograph and a link to an actual photograph of the site where the accident occurred.)
Witnesses said they heard a low-flying aircraft but couldn’t see the plane due to the fog.
They further stated that the engines sounded normal and that there was no change in the engine sounds from the time they first heard the aircraft until the sound of explosions was heard approximately 1 minute later.
The weather was not good: scattered cloud at 1,500 feet, broken cloud at 3,500 feet, overcast at 7,500 feet and light rainshowers. Visibility at Juneau Municipal Airport was given as 15 miles but the visibility on the ground near the crash site was estimated at 60-70 yards (55-65 metres).
Correlation between the CVR readout and the approximate flightpath derived from the flight data recorder traces shows that the first, unmistakable abnormality in the flight’s progress occurred at 1201:03 when the captain told the first officer; “‘kay, you’re Howard,” although the aircraft was actually about 9 NM west of Howard. Since prior co*ckpit conversation indicates that the captain had set the 3530 radial (Howard Intersection) into his CDI, it appears that the crew depended on a display of navigational information that seemed to be correct but was in error by about 450°. Similar erroneous indications of progress along the localizer course are evidence in subsequent intraco*ckpit conversation with the conversation dealing with the passing of Rockledge and Earlow Intersections, although the aircraft, in fact, never progressed as far as Howard.
What this means is that although we don’t know what went wrong with the navigation, the co*ckpit recorder makes it very clear that the crew believed the plane was 11 miles (18.5 km) further along than it was and thus they descended below the safe altitude for the approach. The weather meant that they could not see the terrain below them nor the landmarks which would have alerted them that they were still in the mountains. There is no evidence that the crew ever became aware that they were flying into the mountain range.
The NTSB concluded that there were a number of different possibilities, ranging from malfunctioning equipment to signal interference to operational factions; however there was not enough evidence to support any one of them as the most probable explanation.
Probable Cause
The National Transportation Safety Board determines that the probable cause of this accident was a display of misleading navigational information concerning the flight’s progress along the localizer course which resulted in a premature descent below obstacle clearance altitude. The origin or nature of the misleading navigational information could not be determined. The Board further concludes that the crew did not use all available navigational aids to check the flight’s progress along the localizer nor were these aids required to be used. The crew also did not perform the required audio identification of the pertinent navigational facilities.
That’s not to say that operational issues were the cause but that the crash could possibly have been avoided if the crew had used additional nav aids and especially that the cause could have been better identified if they had checked the audio identification of the VORs.
Neither the aircraft nor the navigational aids were found to have pertinent physical faults, so it does seem quite likely that human factors caused the initial issue. It is refreshing to see that the NTSB did not simply blame the crew. Although the report includes an in-depth analysis of the operational issues which could have led to a basic error being made, they clearly acknowledge that there is no evidence that crew error caused the crash.
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