Re "formal control from the ground": I guess what I meant was when did we first start having the concept of "controlled airspace", which pilots could not legally enter under IMC conditions without communicating with air traffic control.
Really though the main thrust of my question is when did an attitude indicator become required in various situations involving legal flight into IMC, in the United States. As noted above the best answer known so far appears to be
* "still not required" for gliders
* "in 1956" for powered light aircraft not engaged in air carrier operations,
* "by Nov 1 1937 if not sooner" for "Air Carrier Passenger" aircraft involved in "instrument day flying" -- see section 04.532 of the 11/1/37 CAR regs-- this is the earliest edition I've yet found of the regs and the same may have existed sooner.
(
http://ntl1.specialcollection.net/sc...%5CCAR0437.PDF )
* by 04/07/50 there appears to have been still no blanket requirement for all aircraft involved in air carrier operations, including day and night visual operations, to have an attitude indicator or gyroscopic bank and pitch indicator. I have no idea whether this is still true today-- the modern regs are too complex to wade through...
(see parts 4a.457 through 4a.550 in
http://ntl1.specialcollection.net/sc...H%5CCAR450.PDF )
However, well before this time it appears that the "Transport Category" had been established, with more restrictive requirements, including at some point during or before 1947, a requirement for a gyroscopic bank and pitch indicator, without regard to whether operations were visual or instrument. Despite the specific reference to "Air Carrier", it appears that the text below from amendment 04-b6 from 8-19-47 actually applies to this "Transport Category". (Yes, it seems that the regs were already confusing by this time!)
(Begin quote: )
"CAR Amendment 04-b6. Air Carrier bank and pitch indicator. Part 04b of the Civil Air Regulations currently requires under 04b.51 (a) (5) that all airplanes subject to certification under this part be equipped with a nonupsetting type gyroscopic bank and pitch indicator. Service experience with instruments of this type has not been sufficiently extensive to warrant a requirement that this type be installed to the exclusion of other types which, while not completely upsetting, have shown satisfactory service characteristics over a long period of time. It appears, therefore, that safety would be served equally well if instruments which are currently used in airplanes certificated under other airworthiness parts of the Civil Air Regulations are allowed to be used for the present.
Interested persons have been afforded an opportunity to participate in the making of this amendment, and full consideration has been given to all relevant matters presented. Since this is an amendment relieving restriction, good cause exists for making it effective without delay.
Pursuant to the Civil Aeronautics Act of 1938, as amended, particularly 205 (a), 601, and 603 thereof, the Civil Aeronautics Board hereby amends 04b.51 (a) (5) of the Civil Air Regulations (14 CFR, 04b.51 (a) (5) as amended), as follows:
Effective August 19, 1947, 04b.51 (a) (5) is amended by deleting therefrom the words "(non-upsetting type)".
(End quote)
(Source:
http://ntl1.specialcollection.net/sc...H%5CCAR4B6.PDF )
As best as I can guess, this referred to aircraft covered by part 04b of the CAR's, which presumably were the "Airplane Airworthiness Transport Category" regulations, and apparently already existed in 1947. Clearly this is a category more restrictive than the "Air Carrier" operations described by parts 4a.457 through 4a.550 of the 04/07/50 regulations described above.
At present the earliest edition I've found of the complete regs of part 04b, the "Airplane Airworthiness Transport Category" regulations, is 12/31/53-- see below.
By 12/31/53 the regulations for "Airplane Airworthiness Transport Category" specified a gyroscopic pitch and bank indicator, without regard to the type of operations to be conducted (see 4b.603 in
http://ntl1.specialcollection.net/sc...CH%5CCAR4b.PDF )
But as noted above it appears that similar regulations were in effect at least as early as 1947; I just haven't seen a copy of part 04b from before 1953.
Steve S