Four Seconds over Indianapolis - Pull early, pull often! - Safety and Training Programs - Cirrus Owners and Pilots Association

Four Seconds over Indianapolis

Four seconds before impact, the passenger in N91MB pulled the CAPS handle and three people survived although the pilot perished.

Four seconds earlier and maybe all would have survived!

The NTSB investigators reconstructed the flight profile of N91MB and detailed the last moments of Bob Edesses and his family flying N91MB from Eagle Creek to Hilton Head.

Amazingly, the NTSB recovered flight performance data from inside the Avidyne PFD, engine data from the Avidyne MFD, and location data and warning alerts logged in the Honeywell GA-EGPWS terrain warning unit, and reconstructed the flight profile in exquisite detail.

Spinning

The PFD recorded the airspeed and altitude during the spin with much greater detail than the radar track.  N91MB descended in a fully developed spin, rotating 5 times about the vertical axis counter-clockwise.  During the spin sequence, airspeed built up to 120 knots after the second rotation and then slowed to about 90 knots after the fifth rotation.  These airspeeds are substantially below Vpd, the demonstrated parachute deployment speed of 133 knots.

Approximately 20 seconds elapsed from initial roll left at 2400 feet AGL (3200 feet MSL) until the end of recording about one second prior to ground impact (some buffered data would have been lost due to electrical power failure).  The first rotation developed over 12 seconds and then four more rotations took less than 3 seconds each.

From the acceleration data recorded by the PFD, the NTSB determined that a longitudinal deceleration at 528 feet AGL and just four seconds prior to impact coincided with the deployment of the CAPS parachute.

The NTSB report further details the impact velocity at 67 feet/second or 39 knots at a nose-down angle of 60 degrees.

Four seconds!

In that time, the rocket blasts off through the roof of the airplane, knocking out the CAPS cover designed to separate and allow the rocket to deploy the parachute bag.

The parachute comes out of the bag reefed partially open.  A slider ring restrains the parachute to open only a small fraction of its 40-foot diameter until the aircraft slows. This enables the parachute to fully inflate without exceeding the deployment forces that might shred the risers or parachute materials.

Parachute deployment timing

From the test videos of the CAPS system in an SR20, the full deployment of the parachute canopy slowed the plane so that it had no forward velocity.  That takes 7-8 seconds after rocket ignition.

Video excerpts from BRS test videos of CAPS in an SR20

In the first 3-5 seconds, the airplane descelerates with the rear riser folded to position the aircraft in a nose-low attitude that helps stabilize the canopy as it opens and reduce the pendulum effect.  Then the pyrotechnic line cutters release the rear riser and lower the aircraft into a neutral horizontal attitude.

The NTSB factual report states:

"National  Transportation  Safety  Board  (NTSB)  investigators  and  a  representative  of Ballistic Recovery  System,  Inc.  (BRS)  inspected  the  CAPS  parachute  system.  The inspection of the rear attachment  harness revealed that the rear harness was intact and undamaged.  The incremental bridle assembly  was  intact  and  unloaded.    The line cutters had been fired but no aerodynamic load was present  after  the  time  of  cut to break the harness stitches that normally allow the tail of the aircraft  to  drop.    This occurs about 8-9 seconds from system activation.  The nose down angle is about  60  degrees prior to the tail dropping.  Once the tail drops, the nose down angle is about 10 degrees.    The  PFD  data  indicated that the airplane impacted the water about 4 seconds after the system  was  activated.   The altitude at system activation indicated by the PFD data was about 1340 feet msl (528 feet agl)."

What if the decision to activate CAPS was made 4 seconds earlier?

Just four more seconds and the activation sequence would have been complete, the forward velocity reduced to zero, the nose-down attitude reduced to 10 degrees down, and the impact velocity about 17 feet/second or 20 knots.

Pull early!

Comments
  • and What If the decision to activate CAPS was made 1 second later!

    Pull Early!!

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