I have suggested to the NTSB that they investigate the nose down pitch
stops on both vertical gyros to assess any excessive impact damage. In the
investigation of the Northwest Boeing 720B upset accident near Miami,
referred to in an previous letter, there was severe damage to the
nose-down pitch stops as a result of a rapid rotation of the aircraft
about its pitch axis. Incidentially this pitch-up phenomenon is not
accompanied by any increase in aircraft load factor and thus is not
recorded on the flight data recorder! Any pilots reaction to this
instantaneous transition is immediate. The crew on the Northwest Airlines
Boeing 720B were very experienced,  the Captain had 17,000 hours and the
co-pilot had 11,000 hours of flight time. There is no way of knowing what
a radical maneuver of this type can have on the aircraft structure, in the
Northwest accident the aircraft broke apart in the air.  Was there a
radical maneuver prior to the explosion?  Incidently I have not heard from
the NTSB about the suggested inspection of the vertical gyros!  I have
been writing letters to most of the government and private aircraft safety
organizations over the past 30 years since I experienced a pitch-up in a
Boeing 707 in 1965 in visual conditions, trying to alert the industry to
this problem. I am hoping that the internet will be the solution to
getting information out to the public.