Accident Douglas DC-6B SE-BDY,

ASN Wikibase Occurrence # 333493

Date:	Monday 18 September 1961
Time:	00:13
Type:	Douglas DC-6B
Owner/operator:	United Nations - UN
Registration:	SE-BDY
MSN:	43559/251
Year of manufacture:	1952
Engine model:	Pratt & Whitney R-2800
Fatalities:	Fatalities: 16 / Occupants: 16
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	15 km W of Ndola Airport (NLA) - Zambia
Phase:	Approach
Nature:	Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:	Léopoldville-N'Djili Airport (FIH/FZAA)
Destination airport:	Ndola Airport (NLA/FLND)
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
In 1960 the former Belgian colony and now newly-independent Congo asked for United Nations aid in defusing the escalating civil strife. In September 1961, fighting occurred between non-combatant UN forces and Katanga troops of Moise Tshombe. UN Secretary-General Dag Hammarskjöld went to Congo to negotiate a cease-fire. On the morning of September 17 the UN-chartered DC-6 SE-BDY left Elisabethville (now Lubumbashi) for Léopoldville (now Kinshasa). It was hit by bullets fired from the ground at Elisabethville. On arrival the airplane was inspected but only one bullet was found to have hit. It penetrated the exhaust pipe of one of the engines.
The damage was repaired. Security measures were taken at Léopoldville to make it appear that a DC-4, OO-RIC, was actually carrying the Secretary-General. It took off at 16:04 and headed directly to Ndola. The captain of SE-BDY did not file a flight plan and wanted to maintain radio silence throughout the flight for security reasons. The airplane departed Léopoldville at 16:51 for Ndola in the Federation of Rhodesia and Nyasaland (now Zambia). Radio silence was apparently maintained until SE-BDY called Salisbury FIC at 22:02, while still outside the FIR, and requested OO-RIC's estimated time of arrival. The DC-4 arrived at Ndola at 22:35 local time without incident. At 22:40 the crew of SE-BDY reported to Salisbury that it was over Lake Tanganyika and was flying on advisory route 432 at 17500 feet to avoid Congolese territory. The DC-6 descended to 16000 feet and contact was made with Ndola Tower at 23:35 and the crew gave an ETA of 00:20. At 23:47 SE-BDY was abeam Ndola. The airplane descended to 6000 feet in accordance with the clearance from Ndola Tower. At 22:10 the flight reported "lights in sight, overhead Ndola descending, confirm QNH" . Ndola Tower confirmed the QNH and asked the flight asked to report when reaching 6000 ft. No such report was ever received. The instrument approach procedure consists of initial approach at 6000 ft on a track of 280° until 30 seconds after the NDB has been passed. The procedure turn is then made to the right at the same height. On completion of that turn and when on the inbound track of 100° to the NDB the aircraft descends to 5000 ft over the NDB, thereafter descending to the critical height of the aerodrome.
The pilot apparently attempted a visual approach to the airport as the airplane turned right after crossing the airport the pilot continued his approach by a subsequent turn to the left. The DC-6 descended and struck trees at an altitude of 4357 ft asl at a shallow angle when slightly turning to the left at normal approach speed.

PROBABLE CAUSE: "It was strongly urged that the Commission should not conclude that the accident was due to pilot error. Reasons have been given for saying that other suggested causes were not really possible. Reasons have also been given for concluding that the approach was made by a visual descent procedure in which the aircraft was brought too low. It could not be said whether that came about as a result of inattention to the altimeters or misreading of them. The Commission felt it must conclude that the aircraft was allowed, by the pilots, to descend too low. In so doing it struck trees and crashed."
COMMENTS FROM THE UNITED NATIONS:
"The Commission has carefully examined all possible causes of the accident. It has considered the possibility of sabotage or of attack and the material or human failures which could have resulted in an accident. It has found no evidence to support any of the particular theories that have been advanced nor has it been able to exclude the possible causes which it has considered. In this connexion it notes that the United Nations and the Swedish Observers who participated in the work of the Rhodesian Board of Investigation also expressed the opinion that it was impossible to exclude any of the possible causes which they considered or to establish an order of priority among them. With respect to sabotage it has noted that the aircraft was without special guard while it was at N'Djili Airport in Leopoldville and access to it was not impossible. The Commission is aware that there are many possible methods of sabotage. No evidence of sabotage has come to its attention but the possibility cannot be excluded. The possibility of attack from either the air or the ground has also been fully examined. The Commission has found no evidence that an attack of any kind occurred It has also noted the opinion of experts that it is improbable that the plane would have been in the apparently normal approach position indicated by the crash path and wreckage analysis had it been under attack. Nevertheless, it cannot exclude attack as a possible cause of the crash. The Commission has also considered various possibilities of material failure, including technical or structural defects, altimeter failure or fire in flight. A thorough analysis of that part of the wreckage capable of being examined was made by technical experts, including members of the Rhodesian Board of Investigation and United Nations and Swedish observers. The altimeters were examined in the United States by the Civil Aeronautics Board and the manufacturer. No evidence of material failure of the aircraft was found, but this possibility cannot be excluded, mainly because of the destruction of a major part of the aircraft by fire. The Commission also considered various possibilities of human failure. It found no evidence that any of the pilots had been incapacitated. It cannot, however, completely exclude this possibility as some forms of incapacity might not be revealed by a post-mortem examination, It also considered various possibilities of pilot error, including the use of a wrong instrument approach chart or a misreading of altimeters. It noted that the Rhodesian inquiry, by eliminating to its satisfaction other possible causes, had reached the conclusion that the probable cause of the crash was pilot error. The Commission, while it cannot exclude this possibility, has found no indication that this was the probable cause of the crash. The Commission considered the possibility that during the course of a visual or semi-visual approach or through the use of an instrument procedure involving a descending turn, the aircraft might have come below the accepted safety margin of 1 000 ft above ground level. On some landing charts, information concerning exact elevations in the approach area is not provided and should the aircraft have descended below the accepted margin a momentary distraction, either from inside or outside the aircraft, might have caused the pilot to lose the remainder of his margin of safety. The Commission however, has found n

Sources:

ICAO Accident Digest Nr.13

Location

Images:

photo (c) Adrian Begg; near Ndola Airport (NLA/FLND); September 1961