Page:CAB Accident Report, Northwest Airlines Flight 5.pdf/13

 Bates, in letting down to the prescribed minimum altitude to determine whether he might land, exercised sound judgment and a proper degree of caution.

In considering this question it should be observed at the outset that it has become a rather common practice for airline pilots to engage in what is descriptively known as "taking a look". In brief, this practice consists of letting down, when approaching an airport at which the United States Weather Bureau has reported the ceiling or visibility below minimums for which landings are permitted, to the altitude prescribed as such minimum ceiling for the purpose of enabling the captain to observe the condition of visibility and ceiling from the cockpit. If, upon reaching the minimum prescribed ceiling altitude, the captain finds that he has visual contact with the ground sufficient for a safe landing, a landing may be effected. If that proves not to be the case, the captain returns to cruising altitude and continues on to an approved alternate. This practice has not been expressly prohibited by the Civil Air Regulations or otherwise. It is evident, therefore, that neither the failure of the dispatcher to direct Captain Bates to proceed to his alternate, nor the action of Captain Bates in descending at Fargo, constituted a violation of regulations.

It is obvious, however, that even in the absence of any prohibitory regulation the question whether it is proper, under any given weather conditions, to let down for the purpose of determining whether a landing might be made must be decided in the light of all weather factors existing at the particular time and place. When Trip 5 reached the vicinity of Fargo, the continued existence of a critical ceiling was not the only adverse weather factor involved. The existence of a cold front moving eastward had been well established and was known by the dispatcher and Captain Bates. They knew, or should have known, that Fargo was to the rear of this cold front and that icing conditions and perhaps freezing rain would occur at various points, particularly near the base of the overcast in the rear of the front. With only slight variations the temperature at Fargo had remained at, or close to, the freezing point for a considerable period and in addition the dew point had been approximately the same as the temperature. Moreover, the dispatcher and Captain Bates must have realized that the temperature which would be encountered near the base of the overcast in the vicinity of Fargo would be lower than the ground readings at that point. Furthermore, Captain Bates had already encountered ice. The dispatcher and Captain Bates should have realized that a marginal ceiling in combination with-icing conditions constituted a very great hazard to any attempt to land. Under all these circumstances, therefore, the dispatcher, in failing to direct Captain Bates to proceed to his alternate, and Captain Bates, in descending for a possible landing, failed to exercise sound judgment and a proper degree of caution.

Thus far we have determined that the descent for a possible landing at Fargo was unjustified and that Captain Bates and the dispatcher were at fault in that regard. This may be considered to have contributed to the cause of the accident, but in order to determine precisely the probable cause of the accident, we must go further and inquire into the cause of the partial loss of control of the airplane. A careful consideration of the evidence has satisfied us that the partial loss of control was not caused solely by the ice which had been accumulated on the airplane. A collection of ice upon airplane surfaces is not an uncommon experience and, while it is to be avoided to the fullest extent possible by the exercise of great caution, in the nature of things it cannot be eliminated entirely. Although the amount of ice which had been accumulated on the airplane was substantial, experience has demonstrated that aircraft may safely be flown with a far greater-accumulation of ice than that which obtained in this case. The testimony in the record of this accident, as well as general knowledge previously acquired, convincingly shows that the accident was not caused solely by ice. It is equally clear, however, that the amount of ice which had been gathered