When the Boeing 707 was introduced every pilot was trained and made very well aware of the possibility of a trim runaway. The procedure for dealing with this was trained on the simulator and even in the aircraft itself during training flights. On some 707 variants there was also a tendency in some configurations for a slight pitch up at high angles of attack (incidence) when approaching the stall. This was of concern to D.P. Davies who required the fitting of a stick nudger on UK registered 707 aircraft.
I quote below from a Leeham News article which you can access in this link:-
https://leehamnews.com/2019/11/01/a-...-in-the-1960s/
It seems to me that this basic knowledge and associated training became "diluted" over time in some countries and airlines. Had the proper emphasis and training been applied by all operators perhaps the 737Max accidents could have been avoided.
See also this link to listen to DPD talking about certificating the 707 and other early jet types:-
D P Davies interviews on certificating aircraft
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Additional Certification Requirements to the 707 by the UK CAA
Prior to the introduction of the European Aviation Safety Agency (EASA) each country, should it elect to, was responsible for approving each model and variant destined to be operated by their own domiciled carriers. As a result of its own aircraft manufacturing industry the United Kingdom (UK) was in reality the only other country in the world that could effectively complete an independent airworthiness review of an aircraft. Each foreign aircraft that was to be registered with the UK authorities underwent a review of its design and, equally important, was also subject to rigorous flight tests.
In his book
Handling the Big Jets (first published in 1967) D. P. Davies, formally head of the flight test department of the UK Air Registration Board (ARB), now the CAA, describes at length the different stalling characteristics exhibited by aircraft with different wing and tail configurations. He personally test-flew every new jet aircraft model that was destined to fly with UK operators, such as BOAC and BEA. Davies also describes the various control systems that were incorporated on both British and American aircraft that reduced the possibility of a line pilot entering a stall. Details of flying characteristics and the use of automated control systems at high angles of attack are also included.
Davies is best known for mandating the fin of the Boeing 707 be lengthened by approximately 36 inches in order to achieve published Vmcg speeds (minimum control speed on the ground). Boeing ultimately accepted Davies recommendation and, we understand, halted production of the 707 for 10-11 months, whilst a new fin was designed and installed. All existing 707s were then retrospectively modified. A ventral fin was also installed on some variants to prevent ‘fully stalled take-offs’ which the Comet was also susceptible to.
Whilst test flying the 707-400 series at Renton, Davies noted that with the first stage of flap selected, the aircraft had a tendency to pitch up just prior to entering the stall. This was determined to be caused by the inboard leading edge devices, peculiar only to the 707-3/400 series which, when extended, effectively retained lift to higher angles of attack, and moved the Center of Pressure forwards, causing the nose to pitch up. Davies was not comfortable with this pitch up tendency and insisted that all UK certified 707 series aircraft were modified with the installation of a ‘stick nudger’ system.
In his book Davies stated that “
The stick nudger introduces a small force into the elevator circuit which imposes positive stick free stability and removed the otherwise self-stalling tendency”. He goes onto to say that “
as its input is so small all the runaway cases are completely innocuous.”
The ‘stick nudger’ should not be confused with a ‘stick pusher’, which is an entirely different system with a different objective. The stick pusher is typically installed on aircraft with T tail configurations which are susceptible to “super deep” stalls, such as the Bae 146 and Bac 1-11. All those Boeing 727s on the UK register were also modified with a stick pusher.
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