Page:CAB Accident Report, TWA Flight 891.pdf/18

 (c)

-13-

The sheence of a weather station in the Visinity of Saronno does not permit ascertainment of any further data.

Conditions likely to cause disturbances, electric discharges and ice formations *

Because of the frequency of strong upward and downward vertical air currents that accompany them, formations of storm clouds are always accompanied by disturbances, even of great Violence, and the existence

of strong electric charges with wide differences in potential and consequent discharges. Inside these formations, icing will occur at heights above the level of the thermic Zero, which according to the soundings made by the Linate station at 12:00 noon was in the neighborhood of 11,500 ft. However, this altitude may vary inside the storm cloud; hence it is permissible to assume that in our case ice might have formed imediately above 10, 000 ft. As to the highest limit for ice formation,

still on the basis of the hosts soundings, we may assume a height of about 20,000 ft.

Documents and weather information supplied to the crew before departure

The documents and the weather information supplied by the Malpensa air- port weather station to the crew of NA Flight 891 on June 26, 1959 before taking off were the following:

(1) Routing papers, including:

[a] (Anna: VI-l) Forecast chart of significant weather - ICAO Form SW, valid from 2:00 pm. to 8:00 pm. of June 26, 1959 (weather conditions plus pos1tion and type of fronts or meteorological phenomna of particular interest);

[13] (Annex 171-2) Prognostic charts for 700, 500, hOO NIB levels - ICAO

Form P, with validity as above (winds and temperatures at the levels indicated);

[C] (Annex III-3} Landing forecasts covering airports along the route, the

terminal point and alternate airports (Aerodrome Forecasts, ICAO Form A).

(2) Verbal explanations of the documents mentioned above and information on general and local weather conditions based on latest available data.

[3] (Annex VII-h) Excerpts from conversations between aircraft in flight and Eilan Control relating to requests for route changes in order to avoid storm zones;

[b] (Annex v1-5) Statement by the SABENA Co. and their Capt. Caughan who took off from the Malpensa airport on a DC-6B plane at 14:33 p.1n.