The single seat training method creates less instructor liability compared to the amount of liability an ultralight instructor had when 2-seat training ultralights were available under the exemption.
The first reason that is the case is because of a legal term called "line of causality". When there is an accident in a 2-seat trainer, the ultralight instructor is in the direct line of causality. The instructor is always PIC while in the airplane. The PIC has all the liability for the crash because they are directly in the line of causality [or prevention].
In the case of the single seat method, the instructor is not in the line of causality. The student was PIC, not them. The instructor never had direct control of the aircraft. Nor did the student ever start training with the belief that the instructor could exercise control of the aircraft.
One could argue that improper training lead to the crash and, therefore, the instructor was liable. I.e. giving instruction put them in the line of causality and improper instruction caused the crash.
This is barred under the education-malpractice doctrine. The existence of that doctrine is why you can't go back and sue your driver's ed instructor because you had an accident. It's also why the Minnesota Court of Appeals recently overturned a jury that found against Cirrus because the plaintiff's family said the crash was the result of improper education. [See "Aftermath" in the September issue of AOPA Magazine for a review of the case.]
No ski school in America would be able to afford to give instruction if you could claim "education" malpractice when you got hurt during a ski lesson. If you break your leg during a ski lesson, you can't sue the ski school if the instructor never had physical control over your skis.
Anyone that ever instructed using the 2-seat method had a lot more liability than any instructor has using the single place training method. For anyone concerned about their liability while giving instruction, it is a great deal less under the single place method. Under the education-malpractice doctrine it is probably non-existence if you have the student sign the usual disclosures and assumption of risk documents.
-Buzz