Date: 31 Jan 97 14:29:24 From: William Sherriff <firstname.lastname@example.org> Organization: AT&T WorldNet Services
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12018 Caminito Campana San Diego, CA 92128 January 22, 1997 To: Aviation Industry: Subject: Induced Pilot Error and Aviation Industry Ignorance Examples: Engineers failed to include a pitot heat system on the "Kiel" probe of the X-31 aircraft that crashed after ice formed on the probe. Evidently they did not believe there was an icing problem in California? There have been at least three fatal accidents that I am aware of due to pitot-static system icing or blocking. The FAA has still not published a suggested technique for control of the aircraft under these conditions. The Boeing 737-200 series aircraft was designed with a short fuselage and the resultant short longitudinal moment arm requires a large rudder for control of the aircraft in an "engine out on takeoff" procedure. Because of the "uncommanded hard over rudder theory" as the cause of recent accidents involving the Boeing 737, there are now directives to modify and limit the allowable movement of the rudder. This rudder modification directive indicates the possible requirement for a change in the horizontal stabilizer design. The amount of stabilizer control is also affected by the short longitudinal moment arm and this factor makes the Boeing 737-200 series aircraft more susceptible to the "pitch-up" phenomenon! A "pitch-up" is a natural reaction of a swept wing aircraft design to a strong updraft. The vertical component of the relative wind moves the center of lift forward on the wing and raises the nose attitude. This happens on every landing when the aircraft enters ground effect and the weight of the aircraft compresses the air creating a more vertical component of the relative wind The classic example of the weather induced "pitch-up: and the resultant pilot induced upset accident is the Northwest Airlines Boeing 720B (8 feet shorter than a Boeing 707, a significant factor) fatal accident near Miami, Florida on February 12, 1963. After two years of investigation the Civil Aeronautics Board Report, (SA-372, File No. 1-0006 released on June 4, 1965) stated "The probable cause of this accident was the unfavorable interaction of severe vertical air drafts and large longitudinal control displacements resulting in a longitudinal 'upset' from which a successful recovery was not made." The Northwest Airlines crew had trimmed both the stabilizer and the elevators full nose down accompanied by a strong forward control force on the yoke upsetting the aircraft into a vertical dive. This was an experienced flight crew, the Captain had 17,000 hours and the Copilot had 11,000 hours flying time. I would predict that any flight crew would have reacted the same way under these conditions, having received the same basic training in impending stall recoveries. This report should be mandatory reading for pilots, especially those flying swept-wing design aircraft. The NTSB accident investigators and FAA personnel were not aware of this report and the NTSB requested a copy from me. I told them it was available right there in Washington, DC. The present prescribed approach and landing procedure require the pilot to mechanically control a "rate of sink" with the resultant minimum "control sense" feedback. In this approach, because of the nose high attitude required, the pilot does not have the landing area in sight in the final stage of the approach! In this approach procedure the inner ear sensitivity to a steady state rate of sink is greatly reduced. In an article published in "Physics Today" Dr. A. J. Hudspeth, PhD, MD of the Rockefeller Institute, states the following: "Constant velocity, e.g. a constant rate of sink, has little ability to stimulate." A Boeing Company study in the CAB report on the Northwest Airlines "upset" accident near Miami, Florida on, April 12, 1963, states the following: "The aircraft was recoverable from a 95-degree dive at 14,000 feet and 320 knots". >From my experience in a vertical dive (free fall) in a Navy fighter type aircraft I would challenge the Boeing Company to demonstrate the technique for a successful recovery of a swept wing transport type aircraft from a vertical dive. The Northwest crew had 35 seconds to recover from 19,000 feet! The aircraft came apart in the air! In this same report the following statement appears, "Entry into an updraft produces an initial aircraft response to 'weathercock' nosedown into the relative wind. However, it was pointed out that the ultimate effect of the updraft is an altitude and noseup attitude increase." In 36 years of flying I have never experienced any aircraft design pitching down in an updraft, initially or other wise. The aircraft accident investigators of the NTSB rely heavily on the Flight Data Recorder (FDR) readings to establish a "probable cause" for each accident. These readings however do not indicate the actual performance of the aircraft. They are the erroneous flight instrument indications affected by the strong updraft that caused the attitude transition. e.g., The reading in the Northwest Boeing 720B accident near Miami indicated a 9,000 feet per minute rate of climb! In the COPA Airline Boeing 737 accident near Tucuti, Panama the FDR recorded instantaneous, radical, attitude transitions that the Boeing Company stated were impossible for the aircraft to perform! In the Colorado Springs Boeing 737 accident, eye witnesses stated the nose was rising just before the aircraft pitched over into a dive,, (ATC controllers statement). The investigators refused to recognize indications on the FDR that the nose had risen because there was no increase in aircraft load factor indicated on the FDR! In a "pitch-up" there is little or no increase in aircraft load factor, as I experienced in an instantaneous "pitch-up" in a Boeing 707! I am a retired Navy and Airline pilot with 20,000 plus hours of flying time. I believe I am the only pilot that has experienced this particular combination of incidents. A "pitch-up" in a Boeing 707 in visual flight conditions, a true vertical dive (free fall) in a Navy fighter type aircraft, and a crash of a Boeing 707 simulator in an unofficial "pitch-up" exercise.. I have also used a "linear momentum" approach and landing technique, resulting in dissipation of excess kinetic energy prior to an imperceptible landing at less than the aircraft's actual weight. Until the industry addresses the problems associated with the "rate of sink" approach procedures, acknowledges the "pitch-up" phenomenon and provides the required pilot training programs we will continue to experience these accidents. Until this required training is completed if there is a finding of pilot error in these areas they must be referred to as "induced pilot error". William J. Sherriff Captain (Retired) American Airlines, Inc.