July 29, 2009

The fatal connection between a flock of American white Pelicans and a Cessna Citation 500 business jet at 3,100ft over a lake in Oklahoma in March 2008 is the fuel behind some new safety recommendations issued by the US National Transportation Safety Board yesterday.

The collision with one or more of birds, which tend to weigh on average about 20lb according to the Smithsonian’s Natural Museum of History, took out the right engine but more crucially, damaged the aircraft’s wings to the point that it was uncontrollable.

The resulting spiral, simulated by the NTSB below, sent the two pilots and three passengers to their deaths.

After some rehashing of radar data, investigators determined which clutter was most likely the flock of pelicans in the vicinity at the time. Blue dots indicate pelicans while the aircraft’s track after it departed the Wiley Post Airport in Oklahoma is in yellow.

Here’s the ultimate result of the collision…

First, an image from a surveillance video camera in the vicinity.

Then the final outcome…

What can be done?

The NTSB made 10 new recommendations, some dealing with how the aircraft was operated, but others focused on mitigating the increasing frequency with which birds and aircraft are meeting.

The simplest strategy, other than see-and-avoid, is to give pilots an understanding of the bird strike energy for which their aircraft are certified. Under Part 25 certification rules, a Cessna Citation 500 must be able to sustain a hit to the wing of a 4lb bird at cruise speed and be able to continue flying. and perform a safe landing.

The image below shows the damage caused by a 4lb bird at a cruise speed of 287kt…

The empennage must be able to handle an 8lb bird at cruise speeds.

The trick is to figure out how fast the airplane can then hit a 20lb pelican, assuming the pilot obtains information that such birds are in the area.

Based in the laws of physics (kinetic energy = 1/2 * mass * velocity-squared), the equivalent energy of the 4lb at 287kt is 14,586 ft-lb, according to the NTSB.

To stay below that energy, the aircraft would have to be traveling at 128kt or slower when it hits a 20lb pelican, according to my calculations. It’s a large decrease in speed, but one that might be worth considering an aircraft’s brief duration at such low altitudes, given the consequences..

What’s the old saying – “An ounce of prevention is worth a lb of cure”?