Narrative:

I was engaged in local flight at the ZZZ airport in a robinson R44 helicopter. At approximately XA54 I landed to situation out a thunderstorm that was threatening. I began a normal shutdown on the ground. Suddenly at XA56 winds blew with great force so I expedited the shutdown. As the blades slowed; it was impossible to stop the rotor disk from tilting backwards. However; there was no indication of problems and shutdown (master off) was completed appropriately. The storm raged and after 1 min on the ground; hail began to fall. It ranged from pea- to walnut-size pieces. I climbed in the back seat of the helicopter for fear the plexiglas windshield would break from hail. It didn't. Then 10 mins later the storm was over. A thorough preflight revealed surprisingly little damage. Only the top of the rotor appeared to have slight pocking. I elected to fly the helicopter. Startup was normal; nothing out of the ordinary. 15-20 mins of hovering and hover-taxiing revealed no anomalies or problems with flight. A normal takeoff was made and the helicopter was accelerated to cruise speed. I thought; 'this helicopter is a mack truck; tougher than nails.' at cruise speed; however; I began to notice a peculiar force causing the helicopter into a crab. It didn't want to fly coordination. I also noticed that excessive cyclic was required for straight and level flight. I had the sense that something else was incorrect and noticed that the cockpit in front of me was beginning to change shape -- to deform and bend to the side as if a severe side-load was being applied. An immediate landing was made. 3 days later; I had 2 robinson-certified mechanics go over the helicopter. I told them the above story and they checked the main rotor system and upper drive shaft housing. They concluded that the helicopter is airworthy and could be flown. Again; I did a hover check and showed the mechanics how even in a hover the cabin was showing slight signs of flexing. I explained that in forward flight this phenomenon would become more pronounced rapidly and that the helicopter would not fly straight and that nonstandard control position would be necessary. The mechanics suggested that the storm got me spooked and that I was just focusing on something that I never noticed before (the centerline of the helicopter) and had experienced an 'optical illusion.' in turn; I was amazed that both of the mechanics were willing to fly in the helicopter. I refused; however; to take off with them as passenger citing their failure to fix anything. 'Replace something broken and I'll fly it.' I also mentioned an NTSB fatal-accident report where the mechanic and pilot get killed during a helicopter test flight. I have spent a couple days reflecting on this situation. I must conclude that the mechanics are correct when they say they found nothing wrong. (I know; however; they are wrong about this being a perceptual error on my behalf.) so the only visible indication anything is wrong are these tiny dents all over the main rotor. The rotor; while stationary; was pelted with hail; quite a bit; I suppose. There are a bunch of specifications in the robinson maintenance manual that I was looking at today that describe how much damage may be done to the rotor. How big a dent may be. The mechanics say the blades will take a lot of dents and pretty big too. They are right. It depends how far dent is in from the blade tip. My damage appears like it may be in specification though this was not measured by anyone. What the manual does not address is how many dents are permitted. I have so many little dents that they run into other little dents. I am wondering if the cumulative effect of all those little dents act to change the airfoil. If the airfoil is changed it would be to reduce the size of the top airfoil relative to bottom making a semi symmetrical. This change may result in increased flapping in forward flight; crabbing; and severe sideways forces. The robinson manual also addresses the possibility that dents on the top maybe translated into protrusions on the bottom of the blade and this was not previously considered. Having flown the helicopter; I believe something may be significantly wrong and I am continuing to evaluate the damage and its effect on the helicopter's airworthiness prior to further flight. Callback conversation with reporter revealed the following information: the reporter stated that when the 2 robinson technicians returned the aircraft for service with no parts replacement and nothing found wrong he then refused to fly the aircraft. The main rotor blades were removed and sent to the manufacturer for inspection and were found unairworthy and scrapped. The unbroken line of pock marks on the leading edges made the blades unsvcable. The blades were replaced and the aircraft flew normal in every respect.

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Original NASA ASRS Text

Title: A ROBINSON R44 HELI PARKED DURING A SEVERE TSTM INCURRED HAIL DAMAGE TO THE MAIN ROTOR BLADES. WHEN FLOWN IMMEDIATELY AFTER THE STORM THE ACFT DID NOT FLY PROPERLY.

Narrative: I WAS ENGAGED IN LCL FLT AT THE ZZZ ARPT IN A ROBINSON R44 HELI. AT APPROX XA54 I LANDED TO SIT OUT A TSTM THAT WAS THREATENING. I BEGAN A NORMAL SHUTDOWN ON THE GND. SUDDENLY AT XA56 WINDS BLEW WITH GREAT FORCE SO I EXPEDITED THE SHUTDOWN. AS THE BLADES SLOWED; IT WAS IMPOSSIBLE TO STOP THE ROTOR DISK FROM TILTING BACKWARDS. HOWEVER; THERE WAS NO INDICATION OF PROBS AND SHUTDOWN (MASTER OFF) WAS COMPLETED APPROPRIATELY. THE STORM RAGED AND AFTER 1 MIN ON THE GND; HAIL BEGAN TO FALL. IT RANGED FROM PEA- TO WALNUT-SIZE PIECES. I CLBED IN THE BACK SEAT OF THE HELI FOR FEAR THE PLEXIGLAS WINDSHIELD WOULD BREAK FROM HAIL. IT DIDN'T. THEN 10 MINS LATER THE STORM WAS OVER. A THOROUGH PREFLT REVEALED SURPRISINGLY LITTLE DAMAGE. ONLY THE TOP OF THE ROTOR APPEARED TO HAVE SLIGHT POCKING. I ELECTED TO FLY THE HELI. STARTUP WAS NORMAL; NOTHING OUT OF THE ORDINARY. 15-20 MINS OF HOVERING AND HOVER-TAXIING REVEALED NO ANOMALIES OR PROBS WITH FLT. A NORMAL TKOF WAS MADE AND THE HELI WAS ACCELERATED TO CRUISE SPD. I THOUGHT; 'THIS HELI IS A MACK TRUCK; TOUGHER THAN NAILS.' AT CRUISE SPD; HOWEVER; I BEGAN TO NOTICE A PECULIAR FORCE CAUSING THE HELI INTO A CRAB. IT DIDN'T WANT TO FLY COORD. I ALSO NOTICED THAT EXCESSIVE CYCLIC WAS REQUIRED FOR STRAIGHT AND LEVEL FLT. I HAD THE SENSE THAT SOMETHING ELSE WAS INCORRECT AND NOTICED THAT THE COCKPIT IN FRONT OF ME WAS BEGINNING TO CHANGE SHAPE -- TO DEFORM AND BEND TO THE SIDE AS IF A SEVERE SIDE-LOAD WAS BEING APPLIED. AN IMMEDIATE LNDG WAS MADE. 3 DAYS LATER; I HAD 2 ROBINSON-CERTIFIED MECHS GO OVER THE HELI. I TOLD THEM THE ABOVE STORY AND THEY CHKED THE MAIN ROTOR SYS AND UPPER DRIVE SHAFT HOUSING. THEY CONCLUDED THAT THE HELI IS AIRWORTHY AND COULD BE FLOWN. AGAIN; I DID A HOVER CHK AND SHOWED THE MECHS HOW EVEN IN A HOVER THE CABIN WAS SHOWING SLIGHT SIGNS OF FLEXING. I EXPLAINED THAT IN FORWARD FLT THIS PHENOMENON WOULD BECOME MORE PRONOUNCED RAPIDLY AND THAT THE HELI WOULD NOT FLY STRAIGHT AND THAT NONSTANDARD CTL POS WOULD BE NECESSARY. THE MECHS SUGGESTED THAT THE STORM GOT ME SPOOKED AND THAT I WAS JUST FOCUSING ON SOMETHING THAT I NEVER NOTICED BEFORE (THE CTRLINE OF THE HELI) AND HAD EXPERIENCED AN 'OPTICAL ILLUSION.' IN TURN; I WAS AMAZED THAT BOTH OF THE MECHS WERE WILLING TO FLY IN THE HELI. I REFUSED; HOWEVER; TO TAKE OFF WITH THEM AS PAX CITING THEIR FAILURE TO FIX ANYTHING. 'REPLACE SOMETHING BROKEN AND I'LL FLY IT.' I ALSO MENTIONED AN NTSB FATAL-ACCIDENT RPT WHERE THE MECH AND PLT GET KILLED DURING A HELI TEST FLT. I HAVE SPENT A COUPLE DAYS REFLECTING ON THIS SITUATION. I MUST CONCLUDE THAT THE MECHS ARE CORRECT WHEN THEY SAY THEY FOUND NOTHING WRONG. (I KNOW; HOWEVER; THEY ARE WRONG ABOUT THIS BEING A PERCEPTUAL ERROR ON MY BEHALF.) SO THE ONLY VISIBLE INDICATION ANYTHING IS WRONG ARE THESE TINY DENTS ALL OVER THE MAIN ROTOR. THE ROTOR; WHILE STATIONARY; WAS PELTED WITH HAIL; QUITE A BIT; I SUPPOSE. THERE ARE A BUNCH OF SPECS IN THE ROBINSON MAINT MANUAL THAT I WAS LOOKING AT TODAY THAT DESCRIBE HOW MUCH DAMAGE MAY BE DONE TO THE ROTOR. HOW BIG A DENT MAY BE. THE MECHS SAY THE BLADES WILL TAKE A LOT OF DENTS AND PRETTY BIG TOO. THEY ARE RIGHT. IT DEPENDS HOW FAR DENT IS IN FROM THE BLADE TIP. MY DAMAGE APPEARS LIKE IT MAY BE IN SPEC THOUGH THIS WAS NOT MEASURED BY ANYONE. WHAT THE MANUAL DOES NOT ADDRESS IS HOW MANY DENTS ARE PERMITTED. I HAVE SO MANY LITTLE DENTS THAT THEY RUN INTO OTHER LITTLE DENTS. I AM WONDERING IF THE CUMULATIVE EFFECT OF ALL THOSE LITTLE DENTS ACT TO CHANGE THE AIRFOIL. IF THE AIRFOIL IS CHANGED IT WOULD BE TO REDUCE THE SIZE OF THE TOP AIRFOIL RELATIVE TO BOTTOM MAKING A SEMI SYMMETRICAL. THIS CHANGE MAY RESULT IN INCREASED FLAPPING IN FORWARD FLT; CRABBING; AND SEVERE SIDEWAYS FORCES. THE ROBINSON MANUAL ALSO ADDRESSES THE POSSIBILITY THAT DENTS ON THE TOP MAYBE TRANSLATED INTO PROTRUSIONS ON THE BOTTOM OF THE BLADE AND THIS WAS NOT PREVIOUSLY CONSIDERED. HAVING FLOWN THE HELI; I BELIEVE SOMETHING MAY BE SIGNIFICANTLY WRONG AND I AM CONTINUING TO EVALUATE THE DAMAGE AND ITS EFFECT ON THE HELI'S AIRWORTHINESS PRIOR TO FURTHER FLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT WHEN THE 2 ROBINSON TECHNICIANS RETURNED THE ACFT FOR SVC WITH NO PARTS REPLACEMENT AND NOTHING FOUND WRONG HE THEN REFUSED TO FLY THE ACFT. THE MAIN ROTOR BLADES WERE REMOVED AND SENT TO THE MANUFACTURER FOR INSPECTION AND WERE FOUND UNAIRWORTHY AND SCRAPPED. THE UNBROKEN LINE OF POCK MARKS ON THE LEADING EDGES MADE THE BLADES UNSVCABLE. THE BLADES WERE REPLACED AND THE ACFT FLEW NORMAL IN EVERY RESPECT.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.