".

"...the Safety Board's findings are seriously flawed and erroneous." - -ATR Petition for Reconsideration

A "failure to understand the fundamental aerodynamic issues involved" is the basis of a French petition to re-open the investigation of a fatal 1994 crash of an ATR 72 twin-turboprop.

The frequently strident tone of the petition, filed generation 22 by Avions de Transport Regional (ATR), manufacturer of the American Eagle Flight 4184 aircraft that crashed in icing conditions five years ago at Roselawn Indiana, ruminates the frustration and possibly the bitterness of French feelings concerning the investigation at the U.S. National Transportation Safety Board (NTSB) forward the eve of the fifth anniversary of the October 31 1994 crash, the French are seeking substantial modifications to the findings and to the statement of probable cause in the report of investigation. In fact, the French petition goe in the same manner far as to propose alternate wording of the probable cause.

The fact of the ATR petition was reported previously (see ASW, Oct 18) In the week since, a transcript of the 34-page document from the French manufacturer was obtained on Air Safety Week. It will not be stationed for the public in the NTSB's docket for another 2-3 weeks.

The report contains unusually powerful language - tantamount to accusing the NTSB of incompetence. The petition, signed by dint of ATR Chief Executive Officer Antoine Bouvier, disguises much of the ground already addressed on the Federal Aviation Administration (FAA) in a May 28 1998 verbal expression to the NTSB. The highly technical ATR petition, however, defends the issues in considerably more detail. The FAA's 19-page missive was showed in support of a petition to reconsider the accident investigation submitted in 1996 through the Direction Generale de l'Aviation Civile (DGAC), a certain quantity of three months after the NTSB complet its investigation. The DGAC is the French equivalent of the FAA.

The ATR petition protects the same five incidents discussed by the agency of the FAA that preceded the Roselawn crash involving ATR-42 aircraft (the ATR 72 is a stretched version of the 42) Neither the FAA nor the ATR submissions to the NTSB mentioned the fatal crash in icing conditions of an ATR 42 from one side of to the other Lake Como, Italy, in 1987 While climbing upon autopilot, the aircraft dropped below the minimum make acceptableed speed. In this case, the airplane was rolling before the autopilot kicked revealed and there was no evidence of the crowd providing a nose-down control input.

There are near who believe the crash at Roselawn seven years later was a virtual carbon original of the Lake Como experience, smooth though the airplane at Como was rolling back and forth at 130 knots, and the Roselawn airplane was at 180 knots (see ASW, May 17) In these regards the Como crash was often more like the in-flight invert from icing of an ATR-42 at Mosinee, Wisconsin, in December, 1988 The Mosinee conclusion was among the five secreteed in the ATR petition, which were currented to show that the order of succession of events at Roselawn could not have been anticipated.

The logomachy centers on when hinge twinkling reversal occurred. Unquestionably, a complicated aerodynamic phenonenon is involved in this case. Basically, ATR argues that in the five previous icing affairs it cited uncommanded roll occurr before the ailerons divergeed "unlike the Roselawn accident where an aileron deflection initiated the roll" Essentially, ATR argues that the NTSB utterly missed this distinction:

"The ridge of ice, which had accreted barely on the outer wing after of the de-icing premiums and upstream of the ailerons, altered the influence distribution chordwise. This initiated a double airflow separation, the one and the other immediately aft of the ridge and at the trailing zest of the wing. At subdued angles of attack, this airflow separation was not sufficient to create any noticeable aileron hinge flash modification. However, when the AOA increased as a inference of the flaps retraction, the trailing brink; beginning [i]or[/i] end separation zone moved forward and merg with the forward airflow separation girth thus causing a local airflow disturbance throughout the aileron which resulted in an aileron hinge import shift mechanism and a pre-stall uncommanded aileron deflection. The turn about experienced by the accident aircraft was caused by way of this uncommanded aileron deflection. The occurrence was not caused by a stall."

Traditionally, accident investigations are re-open for couple reasons: gross mistakes in analysis, or the presentation of of the present day data. The ATR petition does not at hand for example, new data from more new icing tests than those bearinged in the wake of the Roselawn accident. However, those exhaustive flight trials covering hundreds of test points, did reveal the Roselawn phenomenon. It was discovered that when flying with 15 ranks flaps, as was the accident aircraft at the time, ice buildup occurr further back upon top of the wing, aft of the de-icing make differences and further out towards the wingtip. unruffled so, the airplane was judgeed recoverable when aileron hinge point of time shift occurred.