Lockheed Martin [LMT] on Tuesday reported solid first quarter financial results with strong sales, flat earnings, and strong cash flow, results it said were not impacted by the COVID-19 pandemic.

But the outlook for the rest of the year is “uncertain” and is dependent in part on the “duration and spread” of the ongoing pandemic, and the resulting actions by the federal, state, local and international governments, the company said. The pandemic has disrupted supply chains and financial markets, and restricted travel and transport, all signs of significant impacts on the U.S. and global economy, it said.

Sales in the quarter increased 9 percent to $15.7 billion from $14.3 billion a year ago while net income was level at $1.7 billion. The company’s per share earnings were up slightly to $6.08 in the quarter versus $5.99 a year ago due to a lower share count and easily topped consensus estimates of $5.81.

Higher taxes in the quarter pressured net income. The company’s operating margin slid 2.3 percent to 13.6 percent. Free cash flow was a strong $2 billion.

The sales outlook for 2020 was trimmed less than a percent due to expected COVID-19 impacts “as production and supply chain activities have recently slowed in the Aeronautics business area,” the company said. Sales are now forecast to be between $62.3 billion and $64 billion versus the prior outlook of between $62.8 billion and $64.3 billion.

Guidance for segment operating profit, per share earnings, pension adjustments, and cash flow remain intact but Lockheed Martin cautioned that the road ahead is unclear.

“The corporation’s 2020 outlook assumes, among other things, that its production facilities continue to operate and it does not experience significant work stoppages or closures, it’s is able to mitigate any supply chain disruptions and these do not worsen, and it is able to recover its costs under contracts and government funding priorities do not change,” the company said.

The guidance includes some additional caveats.

One is that it excludes potential non-cash impairment charges related to its investment in the Advanced Military Maintenance, Repair and Overhaul Center (AMMROC) joint venture, which earlier this month lost its only contract for repair and overhaul services for fixed and rotary-wing military aircraft. The joint venture, which consists of EDGE and Lockheed Martin, is reviewing its options on whether to protest the loss, continue as a subcontractor, win new work, or close shop.

Going forward, if AMMROC doesn’t retain any business with its current customer, Lockheed Martin expects the potential for a “significant” impairment charge that could hit earnings as early as the second quarter.

The outlook also doesn’t factor in the U.S. kicking Turkey out of the F-35 fighter program, which the company doesn’t expect to materially impact results this year.

At the operating level, Lockheed Martin’s sales gains were driven by F-35 production, sustainment and development and classified development programs in the Aeronautics segment, hypersonic development programs, fleet ballistic missiles and the Next Generation Overhead Persistent Infrared satellite program in the Space group, and High-Mobility Artillery Rocket System, Guided Multiple Launch Rocket Systems, hypersonic development programs, and the Terminal High Altitude Area Defense and Patriot Advanced Capability-3 missile defense programs in the Missiles and Fire Control segment.

Orders in the quarter were above $15 billion, driving backlog to a record $144.1 billion at the end of the quarter, up $139 million from the end of 2019, marking seven straight quarters of backlog growth.

Ken Possenriede, Lockheed Martin’s chief financial officer, said on the company’s earnings call that it expects to rake in more than $3 billion in bookings above plan this year due to an acceleration of customer orders for the PAC-3.

The earnings call was the last for Chairman, President and CEO Marillyn Hewson, who will be retiring as president and CEO on June 15 when James Taiclet, chairman, president and CEO of American Tower Corp. [AMT] succeeds her. Hewson said the company’s outlook remains bright for Taiclet given the company’s performance, strategy and strong backlog.

She also highlighted Taiclet’s experience in the defense industry with Honeywell [HON] and Raytheon Technologies’ [RTX] Pratt & Whitney division, his two years on Lockheed Martin’s board and 17 years running AMT, and his business acumen. The company’s focus on its customers, profitable growth, execution, and its employees won’t change, Hewson said.