I understand your objection.
Back then, I did not see such procedure in the AFM or AOM...
It was a PanAm "expert old timer F/E - in-house - procedure".
Heard that TWA, and NWA did the same...
xxx
So there is a potential structural fatigue for keeping 5 tonnes in CWT since not in AFM.
And I would be telling you "well... sorry, that is the way they did it..."
However I got something else to justify that there is nothing contrary to the AFM.
xxx
Many 747-100 had a "second career" when converted to 747-100SF cargo...
They just located a side cargo door between L-4 and L-5...
And reinforced the floor as required for the pallet weights.
Then...
It was found that these 100SF were very "nose light" or "tail heavy" when empty.
Boeing solution was to recommend leaving... 5 tonnes in the CWT as ballast fuel.
The fuel (despite being ballast) could be used if need be.
So, as far as I am concerned, 5 tonnes in CWT for ballast or warm fuel is structurally similar.
Even with absence of any note or warning in "the bible"... QED...
xxx
JT, I know PanAm and BOAC were competitors on the Atlantic.
But I am certain that some old BOAC F/Es had a few techniques that were "not published"...
And who knows, Air France and Lufty did same. We spied on each other.
I recall mentioning it to my Sabena buddies over a beer in Brussels.
xxx
Example of another procedure I often did...
Old 747 sometimes have leading edge flaps failing to extend (bleed air).
It is due (supposedly) to cold soaked actuators.
If it happens, requires alternate (electric) extension of LE flaps. Time consuming.
So with that in mind, on long flights, I always operate wing TAI 1 hour before top of descent.
Ever since doing so, LE flaps (warm...?) never fail to extend as required.
That also is not "in the book" - but old timers know how to...
Happy contrails