FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1953
1953 - 0166.PDF
164 FLIGHT MOUNTAINS and an AIRLINER "Saint Kevin'': An Aer Lingus Captain Questions Meteorological Theories By Captain R. N. WHITE AS a witness at the inquiry into the accident to Dakota /% EI-AFL Saint Kevin, and as one who was present during the entire inquiry, I read with great interest the article "Airflow Over Mountains." While not wishing to dispute any of the meteorological theory contained in this article, I do feel that the author, Mr. Yates, jumped to several conclusions not fully supported by the evidence and, perhaps inadvertentiy, used facts about this accident to demonstrate certain meteorological theories without paying sufficient attention to other equally important evidence. Mr. Yates, without qualification, states that the probable cause of the accident was "the encountering of a powerful down-current of air on the lee side of Snowdon which forced the aircraft down into an area of very great turbulence." Pt. VIII, Sec. 53, of the official report is not quite so dogmatic: it says "the Court is inclined to the view that the explanation of the fatality may be found under one or more of the following three heads" (my italics). In other words, the cause of the accident is not positively known, but evidence given suggests three, or a combination of three, possible causes. Let us now look more closely at the possible cause which Mr. Yates has selected. An aftercast of the track made good by the Saint Kevin, produced by the M.C.A. and reproduced as Fig. 2 in Mr. Yates' article, purports to show that the aircraft made good a direct track from Daventry to a point very close to the actual point of impact. The assumptions made in this aftercast are:— (a) The aircraft steered flight-plan courses. (b) It flew at a T.A.S. based on the flight plan. (The flight plan was made out at 145 kt T.A.S., which corresponds approxi mately to 575 h.p.) (c) The wind for this sector of the flight was derived from meteoro logical observations and computations and confirmed by the value calculated from the time taken on six other flights along the Daventry-Nevin section of the route between 1500 and 2200 hours. Assumptions (a) and (b) are obviously open to the gravest doubt as to their accuracy, and are very different from assumptions which an airline pilot would make if faced with the same evidence. Assumption (a)—In view of the navigational facilities at Daventry, Droitwich and Shawbury (not forgetting Gee) it is IN an article in "Flight" for January 2nd, Mr. A. H. Yates dis cussed the official findings on the accident to the Aer Lingus Dakota "Saint Kevin," which, on January 10th, 1952, struck the ground at 1,200ft in Snowdonia. Mr. Yates, who is a gliding expert with a considerable knowledge of meteorology, then related the circumstances to the violent turbulence known to exist in mountainous regions, and concluded by suggesting that present airline safety-heights were inadequate in the light of present knowledge of such phenomena. In this article—originally submitted as a letter for our correspondence columns—Capt. R. N. White of Aer Lingus questions certain of the previous author's deductions. The views he expresses are entirely personal. highly probable that Capt. Keohane altered course before reaching 3 deg W if, in fact, he was off course. It might be of interest to the layman to learn that only a very small percentage of flights follow exactly the courses and ground speeds estimated in flight plans. Assumption (b)—It was the normal Aer Lingus procedure to increase power from 575 to 625 or 650 h.p. to maintain schedule when flying into strong head-winds. At 4,500ft such an increase of power will increase the T.A.S. by approximately 10 kt. Capt. Keohane had made such an increase in power on a flight from Birmingham to Dublin earlier in the same day. Assumption (c)—Pt. VII, Sec. 41, of the official report admits that the wind speed calculated as 60 kt is accurate only to within plus or minus 6 kt. By adding the tolerances in (b) and (c) the ground speed of the Saint Kevin may have been 16 kt faster than is assumed by the court of inquiry, and coupling this with the position reports passed by the Saint Kevin we may ask if Mr. Yates is being accurate or fair in talking about "unexplained errors in navigation" and, in the next sentence, "an error in estimating ground speed was also made." No evidence given before the court proves beyond reasonable doubt that the Saint Kevin was ever more than five miles from its planned track up to its last R/T. message. Pt. VIII, Sec. 49, of the official report reads: "It must be stated at once that except on an 'airway' there is nothing inherently wrong about being knowingly a few miles one side or the other of a planned course without reporting the fact." As an airway is 10 n.m. wide (and the Saint Kevin was not flying on one) it is not unreasonable to assume that an aircraft say 6 to 8 n.m. from a planned track is Capt. White provides this official diagram of tracks, times and other details relevant to the "Saint Kevin" accident.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
