The intercept
  Posted by Poronsky John A. Jr., il y a 5 mois (on 02/17/2018)

Jerry Kemp and I were on Jerry’s FCF Mach run checkout.  This was the 2nd attempt on the aircraft so we skipped the beginning portions of the FCF profile, passed over the Wash ranges and headed out over the North Sea.  Don’t remember the altitudes, but we were following the profile and accelerating through 1.7M when there was a loud “bang” and the aircraft started shaking a bit.  Jerry instinctively pulled the throttles back to slow, but the vibrations increased and got more violent…we pushed back up to 1.7M where it was more or less just a little burble.

A little pre-history…

The “F” Model had issues with the P100 engine periodically “barking” when selecting afterburner.  Several times the result of the momentary stall was violent enough that the aux intake doors would be bent or folded inward.  So, for a period of time from 1972-1979 “ish” where we were restricted from using the afterburner except for takeoff and only after we manually opened the bleed air valves, rubbed the voodoo doll and selected/stabilized stage III one engine at a time.  This “cure” basically meant that the “F” Model was restricted to subsonic flight during peacetime missions… “if we weren’t allowed to go super, we wouldn’t need afterburner.”  Don’t remember any engine modifications or other direct cause for “reversal,” but the restrictions were removed around the 1979 timeframe.  The planes had been restricted for so long a decision was made to take each aircraft through the FCF Mach run prior to releasing it for full up for the masses.

On the first attempt with this aircraft (can’t remember who my right seater was), at around 550KIAS (think we were in the mid-thirties) there was a bang.  Nothing else happened…no engine issues, no vibrations, etc.…the aircraft flew normally.  We returned to Lakenheath and flew a standard straight in.  We got to the de-arm and the crew had us shut down.  The left horizontal slab was gone…nothing there but the I-beam that it used to be attached to.  (And if you’re wondering, the slab gauge was normal through the approach and landing…nothing to indicate anything was wrong.)

GD tech reps determined the cause was a delamination.  There is a “hammer” test that can be done to check for delamination, but it wasn’t done prior to this flight.  As the hammer is tapped along the seams/edges the sound changes indicating where and how much delamination there is.  Once delamination starts moisture enters the structure deteriorating the honeycomb structure.  The additional stress and heat generated during Mach airspeeds heat the moisture enough to generate steam/pressure that somewhere the top or bottom plates opened around the leading edge…and the rest went along for the ride.

After replacing the slab, the hammer tests were performed and maintenance found that the rudder had delamination issues.  The rudder was replaced bringing Jerry and me to the start of this story…

Jerry declared the Mayday and turned back towards the wash area.  We attempted several other decelerations, but less airspeed meant more and more violent shaking…we decided to keep it at 1.7M until we were close enough to land that the plane would hit the water and our capsule would be close enough to the various fishing boats that we would be picked up in a reasonable time.

Radar called to say they had sent one of the alert Lightnings out of Binbrook to provide some type of moral support as we pressed in.  Sometime later we heard the Lightning pilot say he had a visual and would be rejoining to the right wing.  As he came in it looked like a standard rejoin after takeoff…just pulled up into a root position.  He then said he would be taking a “look around” and get back with us…seemed like a long time before he came back on the radio.  I can still remember his tone when he said, “Are you ready to copy?”  I thought he was going to make our ejection decision easy.  Couldn’t believe it when he said the only visible problem was the rudder.  It had “blown apart,” but stayed attached to the vertical stabilizer.  The jagged edges were protruding left and right at various angles and distances causing the vibrations.

We gave him our plan and when we were about 15 miles out from land we pulled to idle and dropped the speed brake…as the plan decelerated the vibrations because so violent all the instruments/front panel was a blur…couldn’t read anything…about the time we hit 0.9M everything “disappeared,” no shakes, no vibrations…just normal feeling and indications on everything. 

The Lightning stayed with us through the landing and as I recall diverted to (name escapes me right now) one of the RAF fields just east of the Wash ranges because of low fuel.

Still remember the rendezvous, 1.7M in the mid-30s like it was nothing…I know from my experience in F-16s that any number of small mistakes/errors would have blown the intercept with very little chance of correcting.  I never found out who he was, but his flying skills were truly outstanding!

Remember the hammer tests…since they replaced the bad one with a “new” rudder, maintenance didn’t think it was necessary to perform them…and they didn’t!

I left active duty when my tour was up at Lakenheath.  I was around long enough to fly and check out a couple others in the first “SIS” modified F Model.  Don’t know what happened checking out the rest of the fleet, but I was 2 for 2 bad!

Jack

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