By James Arnold BBC News Online business reporter

Is the sun setting, or rising?

At first glance, the resignation of Phil Condit, chairman and chief executive of Boeing, seems catastrophic news for the aerospace giant.

Coming just a week after his number-two, Mike Sears, was sacked for unethical conduct, Mr Condit's departure looks like an admission that the rot widely diagnosed in Boeing ran right to the top.

The aircraft maker has already been suffering grim market conditions; now, it seems to be drowing under a wave of investigations for dodgy ethics.

So why have its shares - fairly robust performers during this year of crisis - actually risen?

Drawing a (wobbly) line

Mr Condit has tried not to link his resignation directly with the firing of Mr Sears last week.

Mr Condit could have got away with less

Instead, he insisted, he was going in order to clear the way for a new boardroom structure at Boeing, drawing a symbolic line under the affair.

He is unlikely to achieve that.

The admission that Mr Sears hired an Air Force official who was in a position to help Boeing win military contracts has shown that corruption - albeit of a relatively mild sort - had penetrated to the boardroom.

Worse, Boeing faces a Defense Department investigation into an $18bn deal to acquire 100 Boeing 767 planes for use as midair refuelling tankers.

The probe - which is not going to go away just because Mr Condit has departed - follows an admission that the firm obtained 25,000 confidential documents from rival firm Lockheed Martin.

Frozen out

At stake, it appears, is big money. Boeing brought in roughly $15bn from US Government contracts last year, nearly one-third of its overall global revenue.

Military revenues are less stable than they look

Until recently, Boeing had a near-monopoly of US military orders, especially since it took over rival McDonnell Douglas in 1997.

But as US military spending has increased, Boeing's share has fallen: it still gets a slice of most business going, but firms such as Lockheed Martin are muscling in convincingly.

And this year, the government has indicated that it is not afraid of freezing Boeing out further: after the Lockheed spying admission, it cut the firm out of about $1bn-worth of satellite-related orders.

Good example

But the markets' sang-froid may well be justified.

By firing Mr Sears, Boeing actually went much further than it needed to, for what was effectively only a technical breach of corporate ethics.

And by stepping down himself, Mr Condit has shown that he and Boeing take this type of thing very seriously indeed.

True, he was due to retire in 2005, but the gesture is not one that would have occurred to many far more embattled chief executives.

Significantly, too, his successors are to divide the roles of chairman and chief executive - a piece of sound corporate governance that is still far too rare among US companies.

That should send out the right sort of soothing signals to Boeing's government paymasters.

Turbulence

And, crucially, to the markets.

Scandals aside, Boeing faces a tricky strategic future.

Its once-mighty commercial jet business, the source of just under half its revenue, is on the slide.

Feeble demand among cash-strapped carriers is bad enough; but this year, European rival Airbus is also likely to overtake Boeing in unit sales.

And in terms of revenues, Airbus has more than two-thirds of the commercial market, because it is stronger in high-value bigger jets.

Breathing space

For Boeing, the next few months will be crucial.

For Boeing, this one has to fly

Later this month, it begins marketing its 7E7 jet - a replacement for its ageing 767 and 757 models - to airlines.

The firm has already spent $7bn developing the aircraft, albeit in conjunction with Japanese partners, but has yet to pick up an order.

Two previous prestige projects, notably a much-hyped Sonic Cruiser, failed to go into production after failing to pick up orders: the 7E7 has to succeed if Boeing's credibility is to revive.

As Boeing executives trawl the sales conferences, the company will need to hold the patience and confidence of its investors.