PARIS—The Paris Air Show’s muted aircraft-order expectations and preoccupation with the Boeing 737 MAX’s struggles took unexpected turns late June 18 with the stunning announcement of a tentative deal between Boeing and International Airlines Group (IAG) for 200 of the beleaguered model—easily the largest order of the show’s first two days.

The companies said they signed the letter of intent (LOI) at the show. The LOI splits the orders between the MAX 8 and MAX 10 variants. It also is a major blow to Airbus, which is the sole narrowbody aircraft supplier to IAG’s airlines.

“We’re partnering with the Boeing brand. I’ve worked with Boeing for years and it’s a brand I trust,” IAG CEO Willie Walsh said. “We have every confidence in Boeing and expect that the aircraft will make a successful return to service in the coming months having received approval from the regulators.”

Deliveries are planned for between 2023 and 2027, and operators will include British Airways and Barcelona-based Vueling.

The MAX has been grounded since mid-March following two fatal accidents in five months. Boeing is close to finalizing modifications to the aircraft’s flight-control system that is at the center of both accidents—October’s crash of Lion Air Flight 610 and March’s crash of Ethiopian Airlines Flight 302. It is not clear when the 380-aircraft MAX fleet will fly again.

“We are truly honored and humbled by the leadership at International Airlines Group for placing their trust and confidence” both the MAX and Boeing, Boeing Commercial Airplanes president & CEO Kevin McAllister said.

Entering the Paris Air Show, Boeing faced scrutiny about the MAX’s design and its response to the accidents. Company executives have repeatedly reiterated that their top priority is getting the aircraft back in service. Boeing has not booked a MAX firm order since the groundings.

Many pundits were projecting a slow overall week for orders, the traditional but largely meaningless measure of mid-year air show success.

IAG and Boeing changed the show’s tone with one order announcement that is massive in both size and symbolism.