" ... two students would take a [B]onanza or [B]aron out for a day of (usually cross country) flying without a flight instructor on board."
That is not possible under FAA rules for student pilots who hold
only student licenses. Have a look at this:
"A review of the NTSB cases involving students who carry passengers indicate that there are really four categories of violations:
Students who, even though they did not possess a private pilot certificate, believed they had sufficient experience and qualifications to carry passengers and were observed either picking up or dropping off passengers at other airports.
Students who violated an FAR during a cross-country flight, such as improperly entering Class B or Class D airspace, and it was determined during an FAA investigation of this violation that a passenger was on board.
Students who mistakenly believed that they could fly with another student pilot who was approved for solo in that aircraft. The FAA determined that the passenger was the other student pilot.
Students who flew with a private pilot and assumed that the private pilot was automatically PIC. In this situation, the burden of proof is on the student to show the FAA that the other pilot (private or higher) is PIC." (my emphasis)
(
- Flight Training)
If Lubitz already held that FAA-issued PPL (issued on the basis of his German license) at the time that he was training in Arizona then he could have flown a Bonanza along with another student, using his FAA PPL/ASEL. That time would not have counted as "solo" however.
Lubitz would have needed to have a CFI who was sat in the right front seat if there was anyone else with him in that Baron, because he did not have a PPL/AMEL
Lubitz would only have been legal on a Baron (a multi-engine aircraft) for flying under instruction, and for solo flight with a sign-off from a CFI for that. There is no legal way to operate under FAA rules
as the holder of only a student pilot license with anyone else aboard your aircraft unless you have a CFI in the right-hand seat who has access to the flight controls. He is then P1 and you are P3 (pilot under instruction). If you are on an approved solo flight,
alone in the aircraft, then, and only then, are you legal as P1.
Lubitz might have been signed off for solo in the Baron, but that would have precluded having a fellow student along on that flight, because "solo" means exactly that.
In fact, even as a licensed pilot, having someone else along on a flight, even a non-pilot, means that it does not count as a solo flight. If you need X hours of "solo cross-country" then those hours must have been flown with you as the sole occupant of the aircraft, not just with you as the sole manipulator of the controls.
Do I know what I am talking about? I hope so:
FAA:
FLIGHT INSTRUCTOR (Gold Seal)
AIRPLANE SINGLE AND MULTIENGINE
INSTRUMENT AIRPLANE
GROUND INSTRUCTOR
ADVANCED
INSTRUMENT