As the community and the entire sport of racing continues to mourn the loss of the 10 individuals who perished in the crash of the Hendrick Motorsports plane Oct. 24, investigators are trying to determine what happened, while the public is wondering what can be done to make sure it doesn't happen again.

I believe the investigation will answer the question of what happened, and I do not want to jump to conclusions, but one line from a Nov. 5 article in the Observer did catch my attention: "The Hendrick plane was not equipped with a ground proximity warning system, which would have let the pilots know they were dangerously close to the mountain ... ."

Without this warning system, the pilots of the Hendrick plane couldn't know that - beyond the dense fog - a mountain loomed in their path.

This tragedy reveals a disturbing problem with our nation's small passenger aircraft: Many are still not equipped with basic warning systems that could avoid tragedies.

More than five years ago, the Federal Aviation Administration ordered all new aircraft with six or more seats to have terrain warning systems by March 29, 2002. All existing aircraft were to have these warning systems installed by March 29 of next year.

Unfortunately, many passenger aircraft owners have not yet installed these critical safety devices, and still others do not keep them up-to-date. This puts passengers and innocent bystanders on the ground in danger.

In the United States during the past 12 months, there have been 12 instances where aircraft flew into an obstacle. Forty-five people died as a result of these crashes. Of the aircraft involved, two-thirds were required to have modern, updated terrain-avoidance systems on board, but didn't.

One of these incidents was the Hendrick Motorsports crash. It is too early to know whether one of these warning systems could have prevented the Hendrick tragedy, but I suspect it very well could have.

Furthermore, the requirements for warning systems do not apply to helicopters, which fly lower and are therefore even more at risk from terrain and obstacles. Ten crashes involving helicopters flying into terrain have occurred in 2004, killing 35 people.

Tragically, many of these accidents involve medical evacuation helicopters that collide with the ground or with buildings or power lines as they speed to or from a hospital, trying to save a patient's life. This combination of speed and the hazardous environment they operate in has too often been deadly for flight crews, patients and bystanders.

Modern terrain-avoidance systems cost between $20,000 and $60,000 - a fraction of the cost of multimillion-dollar helicopters or passenger aircraft.

We must do more to enhance the safety of flight crews, passengers and patients. We must get these warning systems into more aircraft sooner.

The FAA should insist on full compliance from passenger aircraft operators before the 2005 deadline. And it should require helicopters to be equipped with modern terrain avoidance systems.

Furthermore, a unified common database of all dangerous terrain and obstacles should be created to replace the current patchwork. Many current databases are out-of-date, some are inaccurate, and most are incomplete.

Technology cannot prevent every accident. But we must demand a basic level of safety equipment on board the thousands of planes and helicopters which fly through the skies above us every day.

Lives are being lost needlessly. It is irresponsible to not do everything we can - and to require the FAA to do everything it can - to prevent these tragedies and to save lives.

Jim Hall was chairman of the National Transportation Safety Board during the Clinton administration. He is managing partner of Hall & Associates in Washington.