The phrase "rarely able" is correct and usable in written English.
It is often used to indicate that something is very difficult or unlikely to happen. For example, "He is rarely able to complete a task on time."
Rarely able to switch off completely.
To his chagrin, he was rarely able to ambush guerrillas.
The listeners were rarely able to detect the switchovers.
Bigger, more generic services are rarely able to achieve this profile or these 'self-referrals'.
Women can improve their status by "marrying up"; men are rarely able to do so.
The new management of these enterprises was rarely able to keep them alive.
But except in our favorites, we were rarely able to discern specific fruit flavors.
I was rarely able to function for more than a few hours a day.
POPE JOHN PAUL II, frail with Parkinson's at age 83, is rarely able to celebrate mass.
The Giants' wide receivers were rarely able to shake their defenders.
During our stay, we were rarely able to detect the nearby hills from our apartment window.
