Shares of Boeing Co. BA, -1.94% and Honeywell International Inc. HON, -0.89% dropped around 0.3% each in the late session Tuesday following news that the U.S. Army has grounded its entire fleet of Chinook helicopters due to risk of engine fires out of an “abundance of caution,” The Wall Street Journal reported. Army officials said they know of a few engine fires involving the helicopters, resulting in no injuries or deaths. The aircraft are Boeing-made with Honeywell-made engines, according to the report. In an email, Honeywell said non-Honeywell O-rings not meeting its specifications had been installed in some engines during routine maintenance. Honeywell said the suspect O-rings have been identified and isolated, and the company is working with the Army to supply replacement parts that meet its specifications. Boeing declined to comment, saying it was referring questions to the Army.