MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

[spornrad]

Originally Posted by Bergerie1

spronrad,

I think you will find that D P Davies required the stick nudger on the B707-320s registered in the UK (page 262, Handling the Big Jets). He also required a stick nudger on the 747s registered in the UK - it worked a treat.

I always wondered why Boeing did not fit one to the 737MAX.

Merci beaucoup!
From the Leeham article: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.”