CIVIL AERONAUTICS BOARD |
ACCIDENT INVESTIGATION REPORT |
Adopted May 23, 1949 Released May 24, 1949 |
AMERICAN AIRLINES, INC-CHICAGO, ILLINOIS-MARCH 26, 1949 |
An American Airlines DC-6, NC 90736 operating as Flight 6 from Los Angeles to Chicago, struck a power line during an ILS (Instrument Landing System) approach to the Chicago Municipal Airport at 1926CST, March 16, 1949. An emergency pull-up was made and the flight proceeded to Indianapolis where a normal landing was effected at 2029. No one was injured and the aircraft sustained no damage. |
Flight 6, piloted by Captain Ray D Wonsey with H. D. Schmidt serving as co-pilot and S. V. Ballard as flight engineer, arrived in the Chicago area at 1825. Due to weather conditions and other traffic at Chicago, the flight was delayed for 57 minutes, following which it was cleared to start an ILS approach from the outer marker at 1924. The official weather for Chicago Municipal Airport at 1915 was-ceiling 400 feet, visibility 3/4 mile, fog, smoke, wind north 3 mph. The airplane arrived over the outer marker at 1922 1/2 at an altitude of approximately 3,500 feet M.S.L., from which a steep right turn and rapid descent were executed in order to return to and pass over the outer marker on time and at the required approach altitude of 2,255 feet M. S. L. The flight left the outer marker at the proper time but at an altitude 500 to 600 feet higher than that required. In order to lose this excess altitude before passing the middle marker, the rapid descent (calculated to have been approximately 1,300 feet per minute at an air speed of 130 mph) was continued without regard to glide path indication. Captain Wonsey stated that tie started slowing his descent when his altimeter registered 350 feet above the airport level but that the airplane descended slightly below an altitude of 300 feet before descent was checked. One and three-quarters miles short of the airport and before reaching the middle marker, the airplane struck the second of two parallel wires 48 feet apart and approximately 145 feet above the field elevation. These wires are located 381 feet below the ILS glide path. The location and height of this power line are shown under a "Caution" note on the Company's Chicago ILS chart. Power was immediately applied for a quick pull-up, the Captain declared an emergency and proceeded to Indianapolis. Two minutes after this incident occurred the weather for Chicago Municipal Airport was practically the same as that reported at 1915-overeast, ceiling 400 feet, visibility 3/4 mile, fog, smoke, wind NNP, 3 mph American Airlines' weather minimums for a DC-6 ILS approach to Chicago Municipal Airport are-ceiling 300 feet, visibility 3/4 mile. |
GCA (Ground Control Approach) at Chicago Municipal Airport was monitoring the ILS approaches and initiated calls to Flight 6 several times that it was los with reference to the glide path. Captain Wonsey stated that due to poor reception he heard none of these warnings and was not even aware that his approach was being monitored. Copilot Schmidt stated that he heard the final warning but not in time for any action to be taken before the airplane struck the power line. |
Immediately after the difficulty experienced by Flight 6, the ILS glide path and localizer were checked and found to be operating normally. Approximately two hours later two scheduled air carrier flights were monitored by GCA and the glide path was found to be normal. Altimeters from NC 90736 were checked after the landing at Indianapolis and were found to be well within tolerances check of the ILS equipment installed in the airplane showed it to be functioning normally with the exception of one defective tube in the glide path receiver. This defective tube could cause intermittent operation of the receiver but could not cause erroneous readings. Captain Wonsey stated that insofar as he knew his instruments functioned properly during the approach and that during the descent and at the time of impact with the wire, his ILS indicator showed that he was below the glide path. As the second of two parallel wires of equal height was struck, it is obvious that while the airplane may have been in a level attitude it was still descending at the time of impact. There was no damage to the airplane and the only indications it bore of impact with the power line were imprints of the wire on the tires. |
The airplane, carrier and crew were properly certificated for the flight involved. Captain Wonsey's service with American Airlines covers a period of over twenty years. His total time as pilot is approximately 19,000 hours, 600 or more of which were accumulated in the type of aircraft involved. He had successfully accomplished line and instrument cheeks on February 6 and February 26, 1949, respectively. First Officer Schmidt had been employed by Airlines for about nine years. During this period he had served both as Captain and First Officer and had accumulated approximately 9,000 hours of flying time. |
The Board determines that this incident resulted from failure of the flight to maintain sufficient altitude to clear obstructions during an instrument approach. |
BY THE CIVIL AERONAUTICS BOARD |
/s/ JOSEPH J, O'CONNELL, JR |
/s/ OSWALD RYAN |
/s/ RUSSELL B. ADAMS |
Josh Lee and Harold A, Jones Members of the Board, did not participate in the adoption of this report. |
FOOT NOTES: |
* All times referred to herein are Central Standard and based on the 24-hour clock. |