Royal Aero Club Certificates
Obviously, the first place to start is with the Aero Club Certificates and their holders. These details can be found at various locations:
Wikipedia
Graces Guide
Royal Aero Club Index
Graces Guide also provides details of the following early Royal Aero Club Certificates :
Aeronaut's Certificates
Airship Pilot's Certificates
Dirigible Pilot's Certificates
Special Certificates
And also the early Aviator's Certificates from the following countries: Austria; Demark; France; Germany; Russia; Sweden; Switzerland; USA
Finally on the subject of the Royal Aero Club Aviator's Certificates, the Royal Aero Club Index Cards and Certificate Holders photograph album can be accessed on ancestry.com here.
On Line Resources
Unfortunately time and resources prevents this author accessing archival material that is not online or in my personal library. I unashamedly admit to using other web sites, particularly Wikipedia when applicable, as starting points for these biographies.
Ancestry.com provides a great deal of personal information.
The 1933 edition of Who's Who in British Aviation also provided further details for those still active at that time.
For certificate holders in the Military, more online resources are available:
Royal Navy, RNAS and RAF Service Records are mostly available for download from the National Archives :
ADM-188 - Royal Navy Registers of Seamen's Services (1853 to 1924)
ADM-196 - Admiralty: Officers' Service Records (1756 to 1956)
ADM-240 - Royal Naval Reserve: Officers' Service Records (1862 to 1964)
ADM-273 - Royal Naval Air Service: Registers of Officers' Services (1906 to 1918)
ADM-337 - Royal Naval Volunteer Reserve: Records of Service, First World War (1894 to 1922)
ADM-339 - Admiralty and War Office: Royal Naval Division: Records of Service (1914 to 1919)
ADM-340 - Royal Navy, Royal Naval Reserve, Royal Naval Volunteer Reserve and Women's Royal Naval Service: Officers' Service Record Cards and Files (1880 to 1960)
AIR-76 - Air Ministry: Department of the Master-General of Personnel: Officers' Service Records (1918 to 1919)
For the most part, Army records are not yet digitised and would require access to the archives to examine.
Another main source of Military service information are the Army, Navy and RAF Lists. Many of these are available online via the National Library of Scotland.
They may also be found under ancestry.com's sister subscription site Fold3.com
Military promotions, honours and awards are published in the The Gazette
Two excellent relevant online general British Military Aviation resources are :
Andrew Pentland's Royal Flying Corps website, which accumulates a wealth of raw data on men and machines from a large variety of archival resources.
Malcolm Barrass' Air of Authority website, covering the organisation and senior personnel in the RAF in significant detail.
Traditional Resources
Early aviator's activities were widely reported in contemporary editions of both The Aeroplane and Flight magazines.
Biographical details of some RFC and RNAS airmen can be found in various copies of Cross & Cockade magazine.
Harald Penrose's books on the history of British Aviation are a source of anecdotal details and some biographical data:
British Aviation, The Pioneer Years, Harald Penrose (Putnam, 1969
British Aviation, The Great War and Armistice, Harald Penrose (Putnam, 1969)
British Aviation, The Adventuring Years, Harald Penrose (Putnam, 1973)
For those aviators who were then or later involved with aircraft design and/or manufacturing, the following provided much information :
The Putnam series of British aircraft Manufactures (some 20 books covering Airspeed to Westland)
The Wight Aircraft, Michael H Goodall (Gentry Books, 1973)
From Sea to Air - the Heritage of Sam Saunders, Albert E Tagg and R L Wheeler (Crosspoint, 1989)
British Light Aeroplanes 1920-1940, Arthur W J G Ord-Hume (GMS Enterprises, 2000).
British Aircraft Before The Great War, Michael H Goodall and Albert E Tagg (Schiffer Publishing Ltd., 2001)
For Military personnel, the following give some amount of biographical and military organisational details :
The Birth of the Royal Air Force, Ian M Philpott (Pen and Sword, 2014)
A Contemptible Little Flying Corps, I McInnes and J V Webb (Naval and Military Press 2009)
Flying with the Larks - The Early Aviation Pioneers of Larkhill, Timothy C Brown (The History Press, 2013)
Kingsnorth Airship Station - In Defence of the Nation, Tina Bilbé (The History Press, 2013)
The Royal Air Force: Re-Armament 1930 to 1939, Ian M Philpott (Pen & Sword, 2006)
R.F.C. H.Q. 1914-1918, Maurice Baring (Tannenberg Publishing, 2015 originally published 1920)
Royal Flying Corps Handbook 1914-18, Peter G. Cooksley (The History Press, 2008)
The Royal Navy's Air Service in the Great War, David Hobbs (Seaforth Publishing, 2017)
The Royal Naval Air Service During the Great War, Malcolm Smith (Pen and Sword, 2014)
Testing to the Limits - British Test Pilots Since 1910 (Volumes 1 and 2), Ken Ellis (Crecy Publishing, 2015 & 2016)
Through Adversity, The Story of Life in the RFC and RAF Through Three Operational Pilots, Alastair Goodrum (Amberley Publishing, 2020)
Trials, Trouble and Triplanes - Alliott Verdon Roe's Fight to Fly, Philip Jarrett (Ad Hoc Publications, 2007)
The War in the Air, Walter Raleigh (Vol 1) and H A Jones (Vols 2 to 6), (The Clarendon Press, 1922 to 1937)
And finally there are the biographies :
Airy Somethings - The Extraordinary Life of Aviation Pioneer Horatio Barber, Terry Grace and Maggie Wilson (Self-published, 2019)
Claude Grahame-White, Graham Wallace (Putnam, 1960)
The Flight of Alcock and Brown, Graham Wallace (Putnam, 1955)
Frank McClean, Godfather to British Naval Aviation, Philip Jarrett (Seaforth Publishing, 2011)
Howard Pixton, Test Pilot & Pioneer Aviator: The Biography of the First British Schneider Trophy Winner, Stella Pixton (Pen and Sword, 2014)
Pure Luck - The Authorized Biography of Sir Thomas Sopwith 1888 1989, Alan Bramson (Patrick Stephens, 1990)
Sopwith - the Man and His Aircraft, Bruce Robertson (Harleyford, 1970)
Trenchard - Father of the Royal Air Force, Russel Miller (Weidenfeld and Nicolson, 2016)