The phrase "are often a principal" is grammatically correct and can be used in written English.
It can be used when discussing roles or positions that frequently serve as a primary or main element in a particular context.
Example: "In many educational institutions, teachers are often a principal source of inspiration for their students."
Alternatives: "are frequently a key" or "are commonly a main".
Cogging torque is often a principal source of vibration and acoustic noise in high precision spindle motor applications.
This chapter describes that a typical lamina is often characterized as orthotropic with the principal material directions of each lamina coinciding with the fiber direction and transverse to it.
Although autobiographical in nature, "The Open Boat" is a work of fiction; it is often considered a principal example of Naturalism, an offshoot of the Realist literary movement, in which scientific principles of objectivity and detachment are applied to the study of human characteristics.
Will evaluators, who are often principals or lead teachers, be trained to recognize effectiveness in subject matter not their own?
Arts centres have for years worked closely with councils, who are often their principal funders.
Nurses, particularly those with specialist roles, are often the principal health professionals involved in new service models.
In many of the less-developed countries with authoritarian governments, very extensive controls are imposed on the press, and government-owned newspapers are often the principal sources of political news.
The melting glaciers are often the principal concern of climate change in the Himalayas.
Proprietary campaign settings, together with rulesets, are often the principal creative asset of LARP groups and LARP publishers.
In ophthalmology, as in other specialties, these data are often the principal source of information that patients and clinicians rely on to determine whether to use a newly approved therapeutic.
