If you're a Boeing (BA 1.51%) investor, I come today bearing good news and bad news.

The good news is that Boeing reported its first-quarter financial results on Wednesday, its sales came in ahead of expectations at $17.9 billion, and its stock inched up 0.4% in response. The bad news is... well, pretty much everything else, really.  

Boeing by the numbers

Let's start with earnings. There weren't any. In fact, Boeing lost $1.27 per share in its first fiscal quarter of the year -- $0.20 more than what Wall Street thought it would lose.  

And it wasn't only just earnings as calculated according to generally accepted accounting principles (GAAP) we're talking about, either. Boeing's free cash flow (FCF) for the quarter was pretty miserable, too. Cash generated from operations came in at negative $318 million. Subtract another $468 million for capital spending, and FCF came to negative $786 million -- nearly twice the reported $425 million net loss.

For those keeping track, this was Boeing's third straight money-losing quarter (and Boeing has lost money in eight of its last 10 quarters). It also marked a reversion to negative FCF after Boeing had put together back-to-back positive FCF quarters in last year's second half. (Boeing generated negative FCF in seven of its last 10 quarters, according to data from S&P Global Market Intelligence).

Always darkest before the dawn

And yet, Boeing stock was up on Wednesday, despite the bad news. Now why might that be? Why do investors keep coming back to Boeing (which is up 31% over the past year in a "down" market), despite all the losses it has been (and still is) reporting?

Well, in a nutshell, it's because, while recent results have been pretty dismal, Boeing is promising that things are going to start getting better, and soon -- and Boeing has the receipts to prove it.

Consider that the sole good news Boeing had in its earnings report -- its sales -- was really very good indeed. Quarterly sales at the aerospace and defense giant grew 28% year over year in Q1 after growing 35% last quarter, and a small but positive 4% the quarter before that. That makes for a string of tic-tac-toe, three-in-a-row quarters of positive sales growth -- which, at this point, I think (I hope) we can call a trend of sales growth at Boeing.

Boeing delivered 130 commercial aircraft of various types in Q1 and anticipates delivering a total of between 400 and 450 of its 737 narrow-body airlines this year. Demand for the 737 is so strong, in fact, that Boeing plans to increase its production rate to 38 planes per month later this year as it chips away at a $411 billion backlog that is 4,500 airplanes strong.

As these airplanes roll off the assembly line and are delivered to customers, Boeing will receive cash in return -- enough that the company anticipates growing operating cash flow from negative $318 million (currently) to positive $4.5 billion to $6.5 billion by year-end. With capital spending appearing likely to decline as the year progresses, this should leave Boeing with somewhere between $3 billion and $5 billion in positive free cash flow for the year.

What it means for investors

And this, then, is the real reason investors are flocking back to Boeing stock: not the Q1 results, per se, but the guidance for what investors can expect Boeing to produce over quarters two, three, and four.

Assume that Boeing just scrapes the bottom of its guidance range, delivering $3 billion in FCF this year. At its current market capitalization of $122 billion, that works out to a price-to-free-cash-flow ratio of a bit more than 40x for the stock -- expensive, but perhaps not too expensive for a company that's begun racking up 28% and 35% growth rates for revenue.

Moreover, if Boeing maxes out its FCF predictions and delivers $5 billion in FCF this year, the stock's valuation will tumble to just 24.4 times FCF. For a company growing sales at 28% or 35%, that valuation is going to look pretty cheap, pretty fast.

Finally, consider that over the past 12 months, Boeing's total free cash flow was actually more than $5 billion. (It was $5.1 billion, to be exact, despite Boeing consuming cash in Q1). With that fact in mind, the idea of Boeing ending this year with $5 billion in FCF actually seems quite reasonable.

Long story short, Boeing had a bit of a mixed Q1 -- but the rest of 2023 is starting to look very bright. This, in a nutshell, is the future that Boeing investors are betting on. And this is the reason why investors are still buying Boeing stock.