also: にあって
in; at; during; under (circumstances)
Formal conjunction indicating a situation, time, or condition in which something occurs. Often used in written or formal speech. にあっては is more common than にあって.
非常時にあっては、冷静な判断が求められる。
In an emergency, calm judgment is required.
現代社会にあっては、情報の管理が重
In such an emergency, calm judgment is required.
In modern society, information management is important.
In modern society, the accuracy of information is important.
に当たって marks the moment of undertaking an action ('when doing X'), while にあっては marks the surrounding situation or circumstance ('in such a situation'), so they aren't interchangeable despite both sounding formal.
Derived from the particle に + the て-form of ある (ありて → あって) + topic particle は. Literally 'being in/at', it grammaticalized into a formal conjunction.