CH-46As Breaking up in Flight!!!

[GEORGE CURTIS]

By the summer of 1967 the Marine Corps had ten squadrons of CH-46 Sea Knights. Half were equipped with the early A model and the rest were being equipped with the newer D model. Three of the squadrons were in Vietnam and one was on board the assault ships of the Special Landing Force in the South China Sea. In addition, three of the Corps five remaining UH-34 squadrons were in Vietnam and another was with the Special Landing Force.

On 3 May, a CH-46D crashed at the Marines Santa Anna base in California, killing all four members of the crew. Apparently the main transmission mounting brackets had failed, allowing the front and rear overlapping rotors to intermesh. As a result, all CH-46s were grounded pending inspection and modification. To compound the problem, a CH-46A crashed in Vietnam when the tail pylon, containing the engines, main transmission and aft rotors broke off in flight.

The grounding order was lifted after ten days, but two more CH-46As crashed in June with the loss of six of the eight crewmen. On 30 June a CH-46D at Santa Anna crashed when a rotor blade separated from the aircraft. Miraculously all three of the crew survived. All D models were immediately grounded again while the blades were checked. Still another A model went down in Vietnam three days later, due to failure of the main transmission.

A CH-46 Reliability Review Conference was convened at the Vertol plant in Pennsylvania on 1 August. The Marines denied that the quality of their maintenance crews was to blame and suggested that the fault lay in the rotor blades, drive shaft bearings and excessive vibration of the aft pylon. The wrangling did nothing to prevent the deaths of the five crew of an A model from HMM-262, when it lost its tail pylon at 3,000 feet on 31 August. The next day, a tail pylon separated from a Sea Knight as it was landing, but the crew walked away from the crash.

In October, the first Sea Knights arrived at Okinawa from Vietnam for a repair and modification program. A total of 325 A and D models underwent extensive overhaul amounting to 1,000 man hours each, including the strengthening of structural members in the aft pylon and along the ramp closure area and modifications to the engine and transmission mountings. To alleviate the drastic shortage of helilift caused by these problems, ten additional CH-53s and 23 UH-34s were shipped to Vietnam and 31 UH-ls were borrowed from the Army.

The exact causes of the problems encountered by the CH-46 were never pinpointed with accuracy and complete assurance. There is no doubt that some blame was attributed to the extensive modifications made to the YHC-IA in order to sell it to the Marine Corps. The blade folding mechanism imposed new loads on the transmission and fuselage. The widening of the ramp door and the resulting smaller support on the sides of the fuselage for the 'shelf' on which the main components were attached, would have weakened the structure of the aircraft and more powerful engines would have added to the strain. Regardless of the exact cause of the problems, the modification program corrected the problem.

Source:

Vietnam-the Helicopter War
by: Philip D. Chinnery

[Walt]

In may of 67 HMM262 lost ET27 on a milk run to Ky Ha from Marble Mt. the 4 man crew was killed . We lost another one ET49 in the Ah Shau in June of 67 no one was hurt the aft pylon seperated on landing . The last one we lost was ET 35 Aug.31st .where ever one was killed. I reenlisdted in Nam and was home in part of July and august . I returned to Marble Mountain on the 31st but no 262 they had went aboard the boat . So I was waiting at the post Office for a ride to the ship , one of our planes stopped at the post office and the crew chief told me about the crash . What a greeting back in country. we rode around on the boat for a few days while they where decideing what to do . We went to Ologapo for R&R then returned to Viet nam to pick up more A/C to take to Okinawa we had 53 46's abord the Tripoli. On the way to Okinawa we made our plans on how we where going to take the A/C apart for the mod team . The other squadrons flew some men to Okinawa to help with the mod. we made to shifts 12 hours each I was the NCOIC of one of the shifts . On Saturday if you worked the day shift after you finished saturday day time you went back to work Sunday night . If you worked Saturday night you where off until Monday morning . In Dec. all the people I came over with went home and I had to pay for the 30 days leave. We finihed the mod the day after Christmas and started loading the birds aboasrd ship for the return to the war . We spent New Years Eve and New Years day at sea . We off loaded at Dang Nang on the 3rd of Jan . The Poor Divels met us there and the next day we flew to Quant Tri. I went home the end od January . During the Mod you could tell who was 262 and who wasn't because ever one busted their butts . We had some very good men there doing that job . I am proud to have been part of it . I'm sure we saved a few lives with that program.
Look at the old bird is still flying and may have to fly for a very long time waiting on the osprey.
Semper Fi Walt Jones

[GEORGE CURTIS]

On July 17, 1967 the men and aircraft of Marine Medium Helicopter Squadron (HMM) 164 returned to the ship, ibecause her entire complement of CH-46A helicopters had been grounded, Tripoli launched the first all-boat landing from an LPH. In spite of swells eight to twelve feet high, a rain squall 30- to 40-knot winds, and visibility frequently less than one-half mile, the boat landings for Operation "Fortress Sentry" came off almost without a hitch. Ashore near the Cua Viet river some seven miles south of the DMZ, the marines moved inland but encountered no enemy resistance until the 23d. Then, artillery and air support quickly extinguished the enemy's will to fight, and the operation was terminated on the 25th The troops reembarked between 25 and 27 September and the task group headed back to Subic Bay for six days in port.

Tripoli returned to Vietnam at Danang early in October and loaded 39 defective CH-46A helicopters for transportation to Okinawa where their tail pylons were to be replaced. Shortly after she departed Danang on 7 October her lookout spied an Air Force F-105 which crashed into the sea about two miles ahead. One of her helicopters flew to the scene, rescued the pilot and returned him to the ship for medical treatment. Not long thereafter, her lookouts caught sight of a second survivor of the crash. By the time her helicopter arrived on the scene, an Air Force chopper had already picked up the man. Tripoli's helo assisted in the operation by taking on board the Air Force crewman who had jumped in to assist the survivor into the lift harness.

[Walt]

The mod team did not replace any aft pylons . They beefed the aft pylon up at frame 410 and some other places. The marines assigned to the mod team removed the engines ,foreward and aft rotor heads and transmissons . A team from Vertol did all the mode work . When the Vertol people finished we put the a/c back together tested then and then sent them back to the squadrons . The first 10 that was done was HMM262 a/c . The Poor Devils took the 10 birds back aboard the Tripoli and went back to sea with the landing team aboard. They operated off the coast of Nam until Jan 3rd when they flew ashore at Da Nang and joined the rest of the squadron from Okinmawa . The next morning the squadron flew to Quant Tre there new home. In oct. Ever one on flight pay boared a C130 and flew to Japan and back to get there flight time . After that we didn't have to fly to get our flight pay they deceided it was motre inporten to work on the a/c.
Walt Jones SEMPER FI

[GEORGE CURTIS]

Walt

Thank you very much for the information. I am sure countless hours of Maintenance was performed by Tireless hard working Marines.

Having hung in there as a UH-34D Crew Chief I can tell you we needed ALL the 46s the Corps could provide. During TET 68 and early 69, it was consistently large loads of troops, supplies and Medevacs. Nothing was more depressing than pulling into a MEDEVAC zone in a UH-34D with 12 Emergency Medevacs and having to leave BROTHER MARINES behind.

It was a heroic effort to get the 46As back into service and to continue to crew them. It cannot be overstated that many lives were saved by these efforts.

[GEORGE CURTIS]

By the summer of 1967 the Marine Corps had ten squadrons of CH-46 Sea Knights. Half were equipped with the early A model and the rest were being equipped with the newer D model. Three of the squadrons were in Vietnam and one was on board the assault ships of the Special Landing Force in the South China Sea. In addition, three of the Corps five remaining UH-34 squadrons were in Vietnam and another was with the Special Landing Force.

On 3 May, a CH-46D crashed at the Marines Santa Anna base in California, killing all four members of the crew. Apparently the main transmission mounting brackets had failed, allowing the front and rear overlapping rotors to intermesh. As a result, all CH-46s were grounded pending inspection and modification. To compound the problem, a CH-46A crashed in Vietnam when the tail pylon, containing the engines, main transmission and aft rotors broke off in flight.

The grounding order was lifted after ten days, but two more CH-46As crashed in June with the loss of six of the eight crewmen. On 30 June a CH-46D at Santa Anna crashed when a rotor blade separated from the aircraft. Miraculously all three of the crew survived. All D models were immediately grounded again while the blades were checked. Still another A model went down in Vietnam three days later, due to failure of the main transmission.

A CH-46 Reliability Review Conference was convened at the Vertol plant in Pennsylvania on 1 August. The Marines denied that the quality of their maintenance crews was to blame and suggested that the fault lay in the rotor blades, drive shaft bearings and excessive vibration of the aft pylon. The wrangling did nothing to prevent the deaths of the five crew of an A model from HMM-262, when it lost its tail pylon at 3,000 feet on 31 August. The next day, a tail pylon separated from a Sea Knight as it was landing, but the crew walked away from the crash.

In October, the first Sea Knights arrived at Okinawa from Vietnam for a repair and modification program. A total of 325 A and D models underwent extensive overhaul amounting to 1,000 man hours each, including the strengthening of structural members in the aft pylon and along the ramp closure area and modifications to the engine and transmission mountings. To alleviate the drastic shortage of helilift caused by these problems, ten additional CH-53s and 23 UH-34s were shipped to Vietnam and 31 UH-ls were borrowed from the Army.

The exact causes of the problems encountered by the CH-46 were never pinpointed with accuracy and complete assurance. There is no doubt that some blame was attributed to the extensive modifications made to the YHC-IA in order to sell it to the Marine Corps. The blade folding mechanism imposed new loads on the transmission and fuselage. The widening of the ramp door and the resulting smaller support on the sides of the fuselage for the 'shelf' on which the main components were attached, would have weakened the structure of the aircraft and more powerful engines would have added to the strain. Regardless of the exact cause of the problems, the modification program corrected the problem.

Vietnam-the Helicopter War
by: Philip D. Chinnery

[Roger Thaht]

YOu know, i have always heard about something called aft hover, and the pilots putting there hands over the pitot tubes to turn it on. I heard it was causing the tail section to rip off, so they got rid of it. Never seen one. Never seen EEDS either, what was that for?

[Joe Reed]

Hover Aft was only seen on "A" model CH-46's, the switch was on the rear on the center console. Sometimes, if bothe pilots were on the controls, for a variety of reasons, they would ask the Crew Chief to engage the Hover Aft. As I understand it, it positioned the rear rotorhead to help the A/C maintain a hover or landing position. Some pretty sharp HAC's figured out that if you came into an LZ pretty fast and pulled power and cyclic, pushed on a rudder pedal AND hit the Hover Aft switch at approx. the same time, you could run out of turns and air speed at about the same time, VERY quickly! Then the troops could disembark, by then your RPM was back up and off you'd go! Done correctly, it was truely a thing of beauty and skill!! It was, unfortunately, hard on parts and airframes. Although not officially attributted to a failure to my knowledge, station 410 could logically be figured to take a large portion ostress during such a manuever. The Hover Aft was done away with (the manual portion) on "D" and subsequent model '46's. On them It would apply automatically when certain landing configurations were met. Again, unfortunately, the balls to the wall-both sticks full up-and push hard on a rudder pedal LZ approach wasn't one of the "automatic configurations", and the famous "buttonhook" turn/approach would be a thing of the past..... It would be for "A" model pilots to talk about during "remember when" conversations. LOL! They were certainly quick LZ entrances though, the only problem was when the driver "misjudged" the LZ and ran out of airspeed and altitude before you got to the LZ or just after you passed it! LOL! Never happened to me, but it did some others and some of the pictures are posted on the gallery herein!
Hope this helps on one of your questions anyway.
Semper Fi
Joe

[mike sullivan]

Roger... If I had to guess as to what caused the problem, I would have to say it was the result of too many "hard" landings. As I recall, the CH-46A had interior lights in the back of the aircraft near the ramp that came on if the pilot had made an extremely bad landing and put too many positive "G's" on the bird.

If those lights came on, and "if" the crew chief had time to check it out, then an exterior/interior inspection of the fuselage was made to determine if the aircraft could be flown safely back to base. Sadly, I think due to certain combat exigencies and hot LZ's, many of those original frogs were flown back to base with crinkles in the skin at station 410. After a subsequent post flight inspection by squadron mainenance personnel, they were given a thumbs up the next day to meet the demands of the flight schedule. Maybe they should have been kept in a down status for a look by the tech reps and not returned back into action quite so fast.

I lost some good friends in those accidents that were discussed above and I have always suspected that some of those hard landings that were made before Boeing's station 410 "fix" were the real cause of those tragic deaths. We may never know for sure, but a lot of rules were bent in order to meet the operational commitments that were laid down on us all each day by the Wing/Group.

Just the thoughts of an old frog driver who was in the very first Ch-46 squadron to fly them in country...adios and Semper Fi....

[Jack S. Warner]

Interesting discussion:

On June 30, '67, I was just returning from a training hop in a "34. We were on the landing mat at MCAS Santa Ana and I was watching a "New" 46 make a touch and go. He touched O.K. but on "The Go" the aircraft twisted, the entire aft pylon came off and became airborne -by itself-. I watched as the pilot and co-pilot were thrown through the windscreen and landed in the grass on the far side of the landing mat. We ran to help and watched as the crew chief came to the door, stunned, dazed and still standing. Crash control showed up and got everyone to sick-bay.

BBBB UUUU TTTT!!!!!
I never wanted to fly 46's after that and turned down the opportunity to transition with 262. I lost a lot of good friends in the 46 debugging and stayed with the trusty 34. I did finally transition to the 46F model with , again, HMM 163 in Santa Ana.
It was nice to fly but not the "Sports" model that the 34 was. Something about the single rotor that you didn't mind wrapping around. Two rotors, that far apart, spinning to a side flare just didn't compute mathematically.

My observations was that the fuselage at 410 was just not strong enough to handle the torque of the two engines. If you will notice that on the Army's 47 model they have sponsoons running the full length of the fuselage, giving it torque resistance.
Don't remember hearing of a 47 twisting its A__ off at the center of torque........

May they all Rest In Peace..................... We tried........

Semper Fi,
Jack

[Top A]

Joe
While attached to MARTD Whidbey Island, Wa supporting HMM-770 we has CH-46D/153346, MN415, with Hover Aft. Only Single program speed trim acft of our 8 acft, was a pain if AIMD did not have a spare part and it needed one. Could not canni from anoher down acft as all others were dual program. Trans ti an HC sqd in 77, but think I saw it in HMM-268 markings in mid 80's. I was not involves with any of the early problems of the acft, but agree with Mike, Hard lnds, Buttohooks, etc most likely caused airframe failure on the early acft.
For all those involved in the early testing and mods on the PHROG Thank You for long hard hours you spent making it safer fir us in later years and those KIDS still flying her today in IRAQ.

[Joe Reed]

Top "A",
Interesting news Top. Never knew that they produced one that way! Bet it WAS fun to Troubleshoot! LOL! Thanks for the kudos, just doing what we all did then...
Semper Fi
Joe

[jejacobs]

I still remember that the "Pucker Factor" was at an all time high as we lifted off on our next flight after losing our first Phrog, and some damn fine Marines, to that malady on 12 MAY 67:

CH-46A - BuNu 147190
Capt. Mitchell - HAC
Lt. Gottschalk - CoPilot
Cpl. Clover - Crew Chief
Sgt. Akstin - Gunner

They were just a couple hundred yards off KyHa beach and only a couple hundred feet over the water when she up-ended and came apart.

Any of us who lost squadron mates, friends, brothers, etc., to the aft pylon failure, probably questioned the "flyablity" of the Phrog at one time or another and maybe had a few choice some "things to say" about Boeing. But as Lt.Gen. Fred McCorkle has said on more than one occasion:

...while certainly sad and regrettable, from it's acceptance into the inventory, to date, that the Phrog, percentagewise has suffered less major accidents due to structural failures than the majority of aircraft in the Navy / Marine Corps...

And, Top A is absolutely correct: THEY ARE STILL FLYING IN COMBAT TODAY.

The Phrog was, and is, a magnificent aircraft, albeit certainly gettting a bit "long in the tooth and grey on the roof" - not unlike most of us, hey?

"Phrogs Phorever"

Semper fi -

Jake

[Joe Reed]

Right you are, Jake! Phrogs Phorever, indeed!
When I queried the Pilot of the Saigon bird in Pensacola in 2002 (great guy Major Andrew Ryan) I came to find out that he was about six months younger than the converted "D" model (converted to an "E") he was flying! I would think that reliability is no longer an issue for our phrog troops and that we did iron out many of those LARGE bugs for them. Such as was our lot in the grand scheme.
Fly on elegant phrogs, we love you one and all!
Semper Fi
Joe
YW-11
HMM-165 '67-'68

[Walt]

Jake you got ever thing right except the Bu number it was 152550,there was no 147 CH46 's . I thought I taught you better then that but then you are getting old . That was a fairly new AC too and it had not been a slick. I would say by the BuNumber 262 received it in Sept or Oct 66. So that would make the AC only 5 or 6 months old.After that crash I had to go to the Morgue and indetify Clover and that was the hardest thing I had to do In Viet Nam . It wasn't like Law and Order where they pull out a drawer , they had Dead Marines on tables all over the place. It was an awful sight , I still can see that place in my mind after all these years. Just think how badit was for the people working there. SF

[Top A]

Joe, This was last in the hover aft block acft. Troubleshooting not a real problem, our biggest problem was convinceing the non 46 pilots, 34, UH/AH1 and converted fixed wing guys that there NO Tracking promblem in the acft. We would get an aft head beat gripe about every 4/5 flights from those that had little knowledge of hover aft.

[jejacobs]

Walt,

I stand corrected on the BU Number. I never did, nor would I now, argue "data" you you.

My Phrog, ET-38 / 152565 was the second to launch on the emergency recovery. By the time we got to the crash site, Bill Clover had been picked up still alive and taken to the Med-Pad. There was debris floating everywhere and we were instructed to pick up as much as possible. We did a water landing, taxied around like a motorboat, I hung out of the starboard door by my gunner's belt. I grabbed as much debris as possible and handed it back to whomever the other crewman was at that time.

Finally the pilot said that we were too sluggish and had to get out of the water. We almost didn't get airborne, ended up taking off like a seaplane and flew just above the water to get back. When we finally parked on the Flight Line, I noticed a HUGE puddle of water under my A/C. We had been washing out my A/C when the call went out for first the available aircraft to launch. Mine was one of the aircraft closest to the OPS Shack, so a couple of pilots jumped in and away we went. We were so intent about getting out there to help our brothers, we did not even do a pre-flight.

Now, you have probably already guessed why the bird was sluggish in the water and the reason for the large puddle when we came back --- THE DRAIN PLUGS WERE STILL OPEN FROM WASHING OUT THE A/C.

You or Big "O" didn't know about that one did ya, Walt?? Who cares now? All we wanted to do was get out there to help. But when all is said and done, we were too late.

SEMPER FI

Jake

[Walt]

It happens Jake Forest Gump said so. Ask "Big O " about the heater cover as it flew by Mr. Fogg's head on the day of the fly over on the Cruise. SF

[Joe Reed]

The guy standing with me, Gerry Rosser, was flying wing on one of the SVN Aft Pylon failures.Don't remember now if he told me Ky Ha or Phu Bai area, but early '67 time frame HMM-165. Rosser has dropped off the face of the earth. Anybody seen or heard from him??
Semper Fi
Joe

http://pic12.picturetrail.com/VOL431...6/17504379.jpg

[Walt]

I think it might have been ET 27 unless I am wrong I think he was in 262. I'm not sure its the same Rosser , but I remembered the name and I looked in the cruise book and there is a picture of a Cpl. G. Rosser.

[jdullighan]

I started at Boeing in September 1967 as an Engineer in Flight Controls and it seemed like everyone in the place was involved in some way in the breakup problem. Internally it was known as "desync". There was no easily definable cause which could be blamed for what happened which makes a solution much harder to find. As one of the earlier posts mentioned there was no single cause for all the accidents. But if anything happened to cause a "desync", a transmission failure or loss of a blade, for instance, the structure usually failed at station 410. If 410 was beefed up then the failure moved to the next weakest point. The ultimate solution was to prevent the failure that caused the "desync" in the first place, some as simple as making sure the pins in the lower ramp were clean and were all the way in. A pin not seating could put stress on the whole back end. Joe Reed mentioned once that I had apoplexy when he flew with the ramp open. That's why.

Boeing threw immense manpower at the problem and they approached the task from many different directions. One of the approaches was to say OK, so a desync happens, what do we need to do to make the accident survivable. First, sensors would be fitted to each rotor head and if the rotor rpm differed by more than a given amount it could be assumed that a desync was about to happen. So far so good, now it gets a bit wild. To prevent the rotor blades from colliding. the rotor planes had to be tilted back, way back. And it had to be done in milliseconds. That would make engaging hover aft at 140 knots seem like a gentle manouvre. But we haven't finished yet. The pilot's reaction to this would be to come forward on the cyclic as fast as possible. Can't allow that, so we disconnect his controls. So here you are, the airplane standing on its tail and no flight controls. You wouldn't have to crash, everyone would be dead from heart failure. Fortunately this proposal died, especially when a quick reliability analysis showed the cure to be worse than the problem. I think the final word came from Flight Test. They wanted to know who we were going to get to test fly this dog since they had no interest in doing so.

Hover Aft in the 'A' model was a manual trim that tilted the rotor plane back allowing the fuselage to remain closer to level on approach. Without it, the nose gets awfully high in a fast approach. It was placarded against use above 70 knots. But pilots found that engaged at cruise it acted like a speed brake. Combined with another unauthorised manouvre, the Buttonhook, it was amazing how quickly one could get into a hot LZ. We'll fix that says the factory, we'll install an interlock so you can't engage it above 70 knots. Oh yeah, says the pilot, watch this. All I have to do is stick my hand out of the cockpit window and the airflow to the pitot tube is masked enough that it seems like I'm going less than 70 knots. In my opinion, it would have been better to have made it possible to engage Hover Aft, it was so effective the pilots would use it anyway if they had to. Needless to say, this opinion was not received kindly by the factory.

By the way, the Chinook was designed by the same people who designed the H-46. It has the best safety record of any helicopter. #2 is the H-46.

[Wayne Stafford]

Interesting Hover Aft incident the summer of 69 with HMM-265 while on the Iwo Jima. Got the info about the initial flight second hand from a crewman. During an approach to MMAF, or where ever, the Hover Aft didn't kick in when applied and the pilot ended up with the stick in his belly. Of course, just prior to touch down the heads programmed back as advertised and a fun ride was had by all but with a safe arrival. The approach to the ship was of great concern but at least the excursion was anticipated. The gripe was written up, the 40 knot relay was found to be defective and the speed trim box replaced. Now the test hop. I asked the pilot if he was ready to take her up and the reply was "No way!!". I then suggested testing the offending system at 5000 feet and I would accompany him. That he agreed to. We lifted off the Iwo, cruised up to 5000 feet a few miles off the coast of MMAF and proceeded to do practice landings. (Fixed wing pilots just don't understand an altimeter at 5000 feet with an airspeed of 0. Just a comment.) Everything functioned correctly and we flew home.

Wayne Stafford

[Joe Reed]

Right you are John!
We sure could get in an LZ in a hurry if we were loaded lightly enough to recover from the maneuver (or if the approach speed was reasonable enough). As a Crew Chief I wasn't ever quite a good enough stick to really fly a buttonhook approach, although I have made some landings with and without hover aft, with HAC approval, to see what the difference was. On the really smooth, quick ones it was a blast!!
John, THANKS for keeping my Aft Pylon on YW-11! We needed it!!
Semper FI
Joe