I was about to ask if the film was completed, but decided to investigate for myself! Wikipedia as follows

”Ex-RCAF pilot Lynn Garrison supplied the aircraft, crews and facilities for von Richthofen and Brown and personally coordinated the flying sequences for Corman’s film. Garrison had purchased the collection of hangars, aircraft, vehicles and support equipment accumulated for filming 20th Century’s top grossing film, The Blue Max, in 1965. The collection included replica Pfalz D-III’s, SE-5s, Fokker D-VII’s, Fokker Dr.I’s, plus Tiger Moths, and Stampe SV4C’s.

Corman used an Alouette helicopter, along with a Helio Courier, for aerial photography, supported by a number of specialized camera mounts Garrison developed for use on individual aircraft. This allowed footage of actors, such as John Philip Law and Don Stroud “flying” the aircraft. In actual fact, Lynn Garrison trained Law and Stroud to the point where they could take off, land the Stampe, and fly basic sequences themselves, from the rear seat, filmed with a rear-facing camera.

Corman used a filming schedule that included so-called Blue Days, Grey Days and Don’t Give a Damn Days so that the aircraft were used no matter what the weather presented.

On September 15, 1970, Charles Boddington, veteran of The Blue Max and Darling Lili shoots, was killed when his SE-5 spun in during a low-level maneuver over the airfield. The next day, during the last scheduled flight on the shooting schedule, Garrison and Stroud were involved in a low-level sequence across Lake Weston, in the Stampe, when a Jackdaw struck Garrison in the face, knocking him unconscious. The aircraft then ran through five powerlines, snap rolled and plunged into the lake inverted. Garrison and Stroud were rescued from the waters. Stroud was uninjured while Garrison required 60 stitches to close a head wound.

The film contains many factual errors:

Von Richthofen is shown flying a Fokker D.VII before flying the Fokker Dr.I, when in fact the Dr.1 came out earlier than the D.VII
Hermann Göring was not in the ‘Flying Circus’, until he took over command of the squadron several months after von Richthofen’s death.
Lanoe Hawker and Roy Brown were never in the same squadron. Furthermore Hawker died in November 1916 and Brown did not begin flying combat missions until March 1917.
Roy Brown and his squadron were flying Sopwith Camels, and not S.E.5s on the day of Manfred von Richthofen’s death
It is heavily debated whether or not Brown really fired the fatal shot to kill von Richthofen

John Phillip Law – Manfred von Richthofen
Don Stroud – Roy Brown
Barry Primus – Hermann Goering
Corin Redgrave – Lanoe Hawker
Karen Huston – Ilse
Hurd Hatfield – Anthony Fokker
Stephen McHattie – Werner Voss
Brian Foley – Lothar von Richthofen
Robert La Tourneaux – Ernst Udet
Peter Masterson – Oswald Boelcke ”