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Safety Recommendation Details

Safety Recommendation A-70-002
Details
Synopsis: ON JANUARY 13, 1969, A SCANDINAVIAN AIRLINES SYSTEM (SAS) MCDONNELL-DOUGLAS DC-8-62, CRASHED IN SANTA MONICA BAY DURING APPROACH TO THE LOS ANGELES INTERNATIONAL AIRPORT. OF THE 45 PERSONS ON BOARD THE AIRCRAFT AT THE TIME OF THE ACCIDENT, THE FATALLY INJURED AND MISSING TOTALED 15, AND 17 PERSONS WERE INJURED IN VARYING DEGREES. DURING THE INVESTIGATION OF THIS ACCIDENT, INVESTIGATOR-IN-CHARGE W. L. LAMB NOTED THAT THE EFFECTIVENESS OF THE LANDING GEAR POSITION LIGHT TWO-BULB "FAIL-SAFE" CONCEPT WAS GREATLY DIMINISHED IN PRACTICE, BECAUSE OF THE FACT THAT EITHER BULBBY ITSELF WOULD COMPLETELY ILLUMINATE THE LIGHT COVER. THUS, THERE WAS INSUFFICIENT CONSPICUITY ASSOCIATED WITH A SERVICE FAILURE OF ONE OF THE TWO BULBS, RESULTING IN FAILURE TO DETECT A FAILED BULB, AND SO, REMAIN UNREPLACED FOR A LONG PERIOD OF TIME. THERE IS NO "PRESS TO TEST" CIRCUIT FOR THE GREEN LANDING GEAR EXTENDED LIGHTS OF THIS LANDING GEAR POSITION INDICATOR. MR. LAMB CALLED FOR CORRECTIVE ACTION SO THAT THE EFFECTIVENESS AND RELIABILITY OF THIS "FAIL-SAFE" ELEMENT MIGHT BE INCREASED.
Recommendation: THE BOARD RECOMMENDED THAT CORRECT ACTION BE TAKEN TO ENSURE A MORE RELIABLE "FAIL SAFE" NOSE GEAR POSITION INDICATION.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: Santa Monica, CA, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: 79692
Accident Reports: Scandinavian Airlines System, McDonnell- Douglas DC-8-62, LN-M00
Report #: AAR-70-14
Accident Date: 1/13/1969
Issue Date: 12/31/1969
Date Closed: 6/25/1970
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: FAA
To: NTSB
Date: 5/22/1970
Response: -From J.H. Shaffer, Administrator: Your letter of 12 January 1970 recommended that the Federal Aviation Administration take corrective action with McDonnell Douglas to ensure detection by flight crews of failed indicator bulbs in DC-8 landing gear position indicators. We described the steps being taken by the FAA Western Regional Aircraft Engineering Division in investigating the suspected deficiencies in our reply of 20 January 1970. We are nm, in a position to report on the findings and conclusions of the Western Region and to discuss the action being taken. Representatives from systems engineering, flight test and air carrier operations participated in a special evaluation of the DC-8 landing gear position indicating system. The system was evaluated on two airplanes both on the ground and in flight with particular attention to the question raised concerning detection of failed indicator bulbs. The evaluation disclosed no unsafe features in the three green/one red, dual bulb indicator system. Failures of single bulbs were simulated under various cockpit ambient light conditions and in each case it was found that the display permitted detection of the inoperable bulb. The cover shield is, incidentally, translucent, permitting observation of the lighting dissymmetry with either bulb failed. Detection of a failure of a single bulb is enhanced by the marked difference in illumination of the affected indicator in comparison with the other indicators on the panel. Failed bulbs can be easily replaced by the flight crew by removing the cover shield with the fingers. Spare bulbs are available in the cockpit and are stored to the right of the flight engineer's panel. The DC-8 backup visual mechanical indexes for safe-down-and-locked landing gear are conveniently located and easily checked. The nose gear mechanical index can be observed through a port in cockpit floor while the main gear indexes are located on the upper wing surfaces just forward of the inboard spoilers. After our evaluation we cannot envision any difficulties with the DC-8 landing gear position indicating system provided normal flight procedures are exercised and check of the backup visual mechanical indexes is followed in the event of any unsafe indication in the gear system, e.g., red indicator on, or any green indicator off. In the course of this evaluation, it was noted that not all airlines specifically call attention to checking for illumination of both bulbs in each indicator cover shield in their "before start" and "before landing" checklists. Although it is felt that such a statement should not be necessary in view of the conspicuity of a failed single bulb, we are taking steps to recommend to the remaining carriers to include this admonition in their checklists. In summary, the reassessment of the DC-8 landing gear indication system has shown the system to perform its intended function, has an adequate backup system, and is in conformance with all other pertinent Federal Aviation Regulations. In view of the above enumerated facts, it is our opinion that the DC-8 landing gear indicating system provides the required reliability and aircraft operational safety.

From: FAA
To: NTSB
Date: 1/20/1970
Response: 1/20/70 FAA reported personnel from their western division have been working closely with McDonnell Douglas to improve the reliability of the landing gear position indicator. McDonnell Douglas instituting a design change to replace all landing gear micro-switches with proximity switches. Further improvements in reliability will be made to the landing gear indication system if required. The final flight production evaluation will be made by FAA specialists, who will look into the landing gear position as indicated by the conspicuity of the two bulbs installed under the plastic shield. The necessity for installing a "press to test" circuit will be one of the many aspects that will be evaluated. Results of tests will be forwarded to the board. 5/22/70 FAA responded stating: representatives from systems engineering, flight test and air carrier operations participated in a special evaluation of the dc-8 landing gear position indicating system. The system was evaluated on two airplanes both on the ground and in flight with particular attention to the question raised concerning detection of failed indicator bulbs. The evaluation disclosed no unsafe features. Failure of single bulbs were simulated under various cockpit ambient light conditions and in each case it was found that the display permitted detection of the inoperable bulb. The cover shield is, incidentally, translucent, permitting observation of the lighting dissymmetry with either bulb failed. Detection of a failure of a single bulb is enhanced by the marked difference in illumination of the affected indicator in comparison with the other indicators on the panel. Failed bulbs can be easily replaced by the flight crew by removing the cover shield with the fingers. Spare bulbs are available in the cockpit. Not all airlines specifically call attention to checking for illumination of both bulbs. Such a statement should not be necessary in view of the conspicuity of a failed single bulb; however, it is being recommended to the remaining carriers to include this in their checklists. In summary, the reassessment of the dc-8 landing gear indication system has shown the system to perform its intended function, and to be in conformance with all other pertinent federal aviation regulations.