As restrictions tightened in Europe amidst rising new coronavirus cases, U.S. stocks went into a tailspin this week. Of course, the aviation sector wasn’t spared, and despite better than expected Q3 earnings, neither was Boeing (BA). The stock ended the week down 14%, further adding to 2020’s poor performance. Expectations were low heading into the quarter’s print, and despite posting a fourth consecutive quarterly loss, Boeing’s third-quarter results came in ahead of Wall Street estimates.Revenue dropped by 29.4% year-over-year, yet at $14.1 billion still beat the Street’s forecast by $140 million. The loss on the bottom line wasn’t as bad as expected, either, with Non-GAAP EPS of -$1.39 beating consensus by $0.55.Boeing reported negative (FCF) free cash flow of $5.08 billion, yet still, the figure was an improvement on the previous quarter’s negative $5.6 billion. However, with so much uncertainty surrounding the aviation industry, Boeing’s hope of turning cash flow positive next year looks a tad optimistic.As a result, RBC analyst Michael Eisen cut his 2021 estimate from FCF generation of $3.9 billion to a cash burn of $5.3 billion. The change is “mostly driven by further build of inventory," which the analyst sees "surpassing $90 BN in early ’21," and "a delay in the timing of liquidating those commercial aircraft.” Eisen now anticipates negative FCF until 1Q22, compared to the prior 3Q21.Boeing announced it plans on cutting an additional 7,000 jobs. The company entered 2020 with 160,000 employees and has already reduced staff by 19,000. The A&D giant said it expects to cut the workforce down to 130,000 by the end of 2021.It all points to an uphill struggle, although Eisen thinks BA can “turn an operating profit in ’21.”“We believe profitability remains a wildcard as the company battles to remove cost out of the system to offset a lack of demand recovery and will largely be dependent on commercial demand improving,” Eisen said. “Longer-term, the structural moves to consolidate operations by up to 30%, investment in efficiencies, and permanently control cost should provide upside as demand recovers.”Further catalysts including the re-certification of the 737-MAX, the “potential incremental orders of commercial aircraft” plus defense contract awards, keep Eisen’s rating an Outperform (i.e. Buy). His price target, at $181, implies a 25% upside from current levels. (To watch Eisen’s track record, click here)BA gets mixed reviews from Eisen’s colleagues yet they lean to the bulls’ side. Based on 8 Buys, 9 Holds and 1 Sell, the stock has a Moderate Buy consensus rating. Upside of ~24% could be in the cards, given the $179 average price target. (See Boeing stock analysis on TipRanks)To find good ideas for stocks trading at attractive valuations, visit TipRanks’ Best Stocks to Buy, a newly launched tool that unites all of TipRanks’ equity insights.Disclaimer: The opinions expressed in this article are solely those of the featured analyst. The content is intended to be used for informational purposes only. It is very important to do your own analysis before making any investment.