Vertical Axis?

"Two crashes still baffle NTSB" Aviation Week and Space Technology, 4 November 1996

"Baffled NTSB deepens probe of USAIR crash" Aviation Week and Space Technology, 14 August 1995

Solving technical puzzles is always a challenge. The root cause may be readily seen or be extremely elusive. Take for example a puzzle that captured the attention of most if not all who fly Boeing 737 aircraft. Two National Transportation Safety Board (NTSB) reports have been issued regarding the tragic loss of life when two of these aircraft uncontrollably spiraled out of the sky.

NTSB/AAR-92/06 report of the 1991 crash of Flight 585 in Colorado Springs, Colorado; published 8 December 1992, stated the cause to be "undetermined".

NTSB/AAR-99/01 report of the 1994 crash of Flight 427 in Aliquippa, Pennsylvania; published 24 March 1999, cites the rudder as "the most probable cause". This report also includes information about Flight 517 which experienced a significant non-fatal event.

NTSB/AAR-01/01 amends the report of the 1991 crash of Flight 585 in Colorado Springs, Colorado; published 27 March 2001, citing the rudder as "the most probable cause".

The NTSB, charged with finding the "cause or the most probable cause" of any accident and recommending changes as required, has done its' job to date. All flight systems were scrutinized. The investigations into these aircraft events suggested that only a rudder control malfunction could be a reasonable cause and the Main Power Control Unit (MPCU) became a principal focus. The other flight control subsystems, ailerons and elevators were ruled out. However, the root cause of the puzzle, what ever it truly is, has not been conclusively identified although its' pursuit has been significant. Questions still exist. Has the "root cause" been identified?

Is it remotely possible that it is not the rudder? If there is a remotely plausible alternative, one would have to take the proverbial look "outside the box". My curiosity overpowered my simple mind and I took a look. Whether the exercise was fruitful or not, I'll let you decide. The result is what I call the Twin Rudder Theory for all those flight system, aeronautic/airframe engineers and airplane mechanics to dwell upon as you drift off to sleep at night, thinking lofty thoughts. Without the resources to prove or disprove my theory, it remains such. At the least, you may agree that an honest application of looking "outside the box" occurred.

Some future event, hopefully non-fatal, or an educated study perhaps, may render the theory factual or pure fiction. For the safety of all who fly Boeing 737 aircraft I hope that eventually, the "root cause" is accurately and finally identified, what ever it is.

First, information in the public domain, of Flight 585, Flight 427 and Flight 517.

Scores of written accounts about these three Boeing 737 Flights, and many other incidents exist.

3 march 1991, Flight 585 (737-200) left Denver at 0923:15A.M. It attained cruise altitude and later descended to approach Colorado Springs, CO. During descent airfarme trim occurred. The aircraft was at an altitude of 1000 feet and airspeed of 155 knots when the event occurred. The aircraft suddenly changed its aerodynamic configuration, which inexplicably rolled it to the right. Prior to the aircraft roll the control tower observed a slight pitch change of the aircraft. Various witnesses reported hearing a loud "snap", popping and crack sound prior to the roll event. It was reported that a cloud or white mist was seen trailing from the aircraft. It was reported that a very bad smelling liquid substance fell from the airplane. The MPCU was substantially damaged.

The Captain and First Officer of Flight 585 were both professionals and in their last 10 seconds of life found themselves in an airframe alien to their capable handling. At 0934:00 A.M. the airframe transitioned abruptly from controlled flight and spiraled into the ground. The aircraft impacted terrain at 0943:41.5A.M. and 25 lives were lost. Many questions were outstanding, without answers.

8 September 1994, Flight 427 (737-300) left Chicago at 1810 P.M. It attained cruise altitude and later descended during approach to Pittsburgh PA. During descent airframe trim occurred. The aircraft was at an altitude of 6000 feet and had airspeed of 190 knots when the event occurred. This aircraft suddenly changed its aerodynamic configuration, which inexplicably rolled it to the left. Witnesses on the ground heard some unusual noise, although the aircraft was six times higher than Flight 585 when the event occurred. It was reported that smoke or mist was seen trailing from the aircraft. The cockpit area microphone recorded a series of "thumps" and "clickety-click" sounds. The FDR plots for longitudinal and vertical acceleration demonstrate an oscillatory variation in amplitude increase over time. Post crash dynamic load tests of the MPCU valve were normal.

The Captain and First Officer of Flight 427 were both professionals and in the last seconds of life also found themselves in an airframe alien to their capable handling. At 1902:57 P.M. the airframe transitioned abruptly from controlled flight and spiraled into the ground 28 seconds later. The aircraft impacted terrain at 1903:22.8 P.M. and 132 lives were lost. Best fit computer simulations of the final 28 seconds of flight never produced a match. Questions are outstanding, without answers.