Including debt, the acquisition is worth $30 billion.
Rockwell Collins, based in Cedar Rapids, Iowa, makes flight deck avionics, cabin electronics and cabin interiors for commercial and military customers.
Farmington, Connecticut-based United Technologies called the businesses complementary and expects $500 million in pretax savings related to the deal. It reaffirmed its 2017 profit estimates.
The companies expect the deal to close by the third quarter of 2018, subject to approval from Rockwell Collins shareowners and regulators.