Speculation abounds following a plane crash. Mechanical flaws, terrorism, pilot error, and weather are the usual suspects. But in the tech age, where even your toaster is digital, IT systems must be added to the list. In the the Air France disaster, there's a particularly urgent need for government authorities to eye the aircraft's on-board computer system as a possible culprit.Even casual observers know that today's airliners are heavily dependent on computers for everything from the autopilot to the in-flight movie. But some systems are more important than others. If the critical ones fail, there can be big, big problems.

Most modern passenger jets, including Airbus 330 such as the one that crashed after takeoff from Rio on Sunday night, are equipped with a computerized guidance system known as an Air Data Inertial Reference Unit. The ADIRU feeds key information like altitude and airspeed data to equally key navigation systems, including the pilots' altimeters and other displays. It also sends data to the autopilot.

Given the above, it's obvious that if the ADIRU is sending bad data to the flight instruments there's real potential for disaster. Never has "garbage in-garbage out" carried such dire consequences.

And the fact is, wonky ADIRUs have been identified as the culprits in several recent near-catastrophes involving Airbus. Last year, for instance, authorities blamed the ADIRU after a Qantas Airbus 330 started porpoising wildly while at cruising altitude. There were 51 passenger injuries, ranging from broken bones to spinal damage, before pilots regained control.

"About two minutes after the initial fault, (the air data inertial reference unit) generated very high, random and incorrect values for the aircraft's angle of attack," the Australian Transport Safety Bureau said in a statement at the time, according to Agence France Presse.

Also last year, the U.S. Federal Aviation Administration issued an Airworthiness Directive warning airlines about an "unsafe condition" associated with ADIRU's aboard Airbus 319, 320, and 321 models. The directive warned that the ADIRU in question was issuing bogus navigational fault warnings that could "result in loss of one source of critical altitude and airspeed data and reduce the ability of the flight crew to control the airplane."

As for the Air France crash, in which it's believed 228 tragic souls perished in the sea off Brazil, the Airbus 330 involved reportedly transmitted warnings to Air France maintenance that its ADIRU was not functioning properly. Did the faulty system ultimately cause the aircraft's experienced flight crew to lose the airplane? At this point, we don't know-but the possibility must be investigated.

ADIRU manufacturers include Honeywell and Northrop Grumman--though it's not immediately clear whose technology was aboard the doomed Air France flight and it's too early to single out manufacturers for any fault related to the accident.

If the ADIRU brought down Air France 447, it would be the largest aviation disaster to be blamed directly on a buggy IT system. As such, it would raise questions about whether today's airliners are overly dependent on computers.

The issue is particularly keen now as the aviation industry's true stick-and-rudder men--fliers, like US Airways' Sully Sullenberger, who cut their teeth in the pre-digital era and who can sometimes still bring a wounded plane down safely through a combination of testicular fortitude and instinct--are hitting retirement age in increasing numbers.

Many of today's younger jet jockeys haven never flown a plane without help from a computer.

It's one thing if Gmail goes down for a couple of hours. It's something wholly different if the software and chips designed to keep a 200 ton tin can straight-and-level as it hurtles along at 500 MPH can't be trusted.

The FAA's tech experts need to get on top of this--now.