As a professional FE from 1971 to retirement,I worked L1049, B707 and B747 (all models to 300).
Prior to commencing my FE training on B707s, I was a licensed ground engineer on Boeing 707s.
In those days our patterns were up to 18 days away,often to places with no or very limited communications back to main base. I often was called on to make maintenance decisions or "guide" the local engineers to get the show on the road. Often there was a need to point the pilots in the right direction as far as in flight defects and suitable diversions to cover engineering problems. A lot of what we knew was never in writing and my company even ran informal monthly engineering meetings to discuss problems and examine what had happened over the last month. All was very definitely not for recording. And the system worked very well, only to come unstuck when pilot only B767 came into being.I have read all the US documents that lead to the demise of the PFEs in the US and the major flaw in them is that they purely look at what switches were operated by the FE. In my opinion the FE did far more than operate a panel
On one of my last B747 trips I advised a captain on an engineering problem that no one on the ground could give timely advice on. I was later told that acting on my advice saved $750,000 Australian due to the aircraft being very tightly scheduled for the next 2 days with no possible replacement aircraft and no suitable tooling for a repair being available on the station we were departing from.
Another advantage of a non pilot engineer was that we could to a degree give an opinion from a very different perspective. We had a different reporting/disciple structure which I think was mentioned by John Beatty in one of his early CRM texts. While on duty we worked for the captain but our long term discipline was via the Chief FE and that meant in an examination of events ,if we were 'right , there was someone backing us up which wasn't always for the case for pilots.
I find it interesting that in the current B737 Max situation ,that the Indonesian aircraft that subsequently crashed ,managed to survive the 1st day with the problem had a 3rd pilot in the cockpit. I had a stab runaway on a B707 very early in my career and picked it as the runaway started,just because I was sitting facing fwd at the time and saw it run well before the pilots saw it.
Overall in my opinion the US operators removed a huge amount of experience from the flight deck many years too soon. When I retired on the scrapping of a number of our B747s, our Deputy chief Pilot said that the FEs had on average made a major contribution to saving at least 3 hull losses/FE. I would agree with that but my score was about 5. In long haul at least I think that we well and truly earned our pay.
Wunwing