WASHINGTON, Jan 17 (Reuters) - JetBlue Airways Chief Executive Officer Robin Hayes told employees on Monday that the planned rollout of new 5G service by AT&T (T.N) and Verizon (VZ.N) on Wednesday is set to "further stress our already fragile air system." Hayes said in a memo the airline is preparing for the "worst" when the new service and new flight restrictions take effect. "While we will do our best to avoid customer disruption, we won’t be able to avoid the impact of this, including significant flight delays, cancellations, and diversions in low visibility flying," Hayes wrote.