United Air Lines Flight 610
| United Air Lines Flight 610 | |
|---|---|
.jpg) A structurally identical Douglas DC-6 from United Air Lines |
|
| Accident summary | |
| Accident type | controlled flight into terrain |
| place | at Crystal Montain, about 18 miles west southwest of Fort Collins |
| date | June 30, 1951 |
| Fatalities | 50 |
| Survivors | 0 |
| Aircraft | |
| Aircraft type | Douglas DC-6 |
| operator | United Air Lines |
| Mark | N37543 |
| Surname | Mainliner Overland Trail |
| Departure airport | Salt Lake City Municipal Airport |
| Destination airport | Denver Stapleton Airport |
| Passengers | 45 |
| crew | 5 |
| Lists of aviation accidents | |
On June 30, 1951, a Douglas DC-6 on United Air Lines Flight 610 deviated from its planned course and crashed about 95 kilometers north-northwest of Denver on a mountainside in the Rocky Mountains . All 50 occupants were killed in the accident.
the accident
United Air Lines' Douglas DC-6 ( registration number : N37543) was on a transcontinental scheduled flight from San Francisco to Chicago . Scheduled stopovers were planned in Oakland , Salt Lake City and Denver. The aircraft took off from Salt Lake City at 12:11 a.m. local time for the Denver leg and climbed to an altitude of 4,600 meters (15,000 feet ). At 1:47 a.m., the aircraft passed the radio beacon in Cheyenne and was allowed to descend to 2,600 meters (8,500 feet).
The crew then initiated a right turn in order to continue to the route point WONT (Intersection WONT). The navigation took place with the help of two Morse signals, which the low-frequency radio beacon (LFR, four-course beacon) emitted in Denver. The pilots initially turned on a south-westerly heading of approximately 210 degrees in order to cut the beacon's beacon at an angle of approximately 45 degrees. The flight should then continue in a south-easterly direction (168 degrees). However, the crew retained the previous heading and continued the descent according to the clearance. At 01:56 a.m., the pilots reported that they had reached the approved altitude of 8,500 feet. The plane was approaching the eastern edge of the Rocky Mountains on the wrong course.
About four minutes later, the Douglas DC-6 hit several treetops with its right wing . The machine left a swath about 150 meters long and hit the eastern slope of Crystal Mountain. The aircraft was completely destroyed on impact. The site of the accident was 2,600 meters (8,500 feet MSL ) about 29 kilometers (18 statute miles ) west-southwest of the city of Fort Collins .
Cause of accident
1. Receipt of the A tone (LFR).
2. After receiving the N-tone (LFR), a left turn should be initiated.
3. On the correct course, the two LFR Morse code merge into one continuous tone.
If the switch is in the wrong position :
4. A-tone is received by the VAR, the N-tone was missing.
The cause of the random flight could not be clearly clarified. The investigators considered it likely that the machine received the Morse code from the Denver Visual Audio Range (VAR) due to an incorrect switch position , but the crew assumed that these came from the Denver Low Frequency Range (LFR).
The crew had set the navigation instruments to the frequencies of these two low-frequency radio beacons because they were to be controlled one after the other. Both four-course beacon sent the identical identifier DEN (Denver) and the Morse code A and N out.
The navigation had to be done first with the help of the Denver LFR radio beacon in order to get from Cheyenne to the WONT route point. The crew should then align their navigation to the Denver VAR. The active radio beacon was selected using an unlit toggle switch, which, together with similar switches, was located at the pilots' knee height. The crew in the dark cockpit could only feel the position of the individual switches, but not see them.
If the switch had been set correctly, the pilots would first have heard the Morse code A , which the Denver Low Frequency Range (LFR) broadcast in the northeast area. In the further course of the flight, the machine would have reached the sector in which the radio beacon was sending its N tone. This tone would have been the signal to initiate a left turn and continue the flight in a southwesterly direction. Then the crew would have aligned the aircraft on a heading of 168 degrees, with both Morse code merged into one continuous tone.
If the switch had been set incorrectly, the crew would also have received the Morse code A , but this came from the Denver Visual Audio Range (VAR). In addition to the identical Morse code, the radio beacon also used the same identifier DEN , so that the pilots would not have noticed any acoustic difference. Because the Denver VAR did not emit an N tone in these squares , one would not have been received until impact.
It remained unclear why the crew did not react to the absence of the N-tone and why the flight in the direction of the Rocky Mountains continued for so long. Investigators suspected that the captain, who had spent most of his flying hours on the Douglas DC-3 and had only recently received a license for the Douglas DC-6, did not take into account the higher speed of this type.
Investigators also believed it possible that the crew made an inaccurate adjustment of the radio compass (ADF), which enabled them to receive the radio beacon at Fort Bridger, which was transmitting on a similar frequency.
In order to avoid future confusion between the Denver LFR and the Denver VAR, the Morse code of the Denver Visual Audio Range (VAR) was added the additional letter V.
Individual evidence
- ↑ a b c d e f Official investigation report (in English): CIVIL AERONAUTICS BOARD, Accident Investigation Report, United Air Lines, Fort Collins, Colorado, June 30 1951 ( Memento of the original from June 10, 2015 in the Internet Archive ) Info: Der Archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
Coordinates: 40 ° 32 ′ 6 " N , 105 ° 24 ′ 48" W.