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ROTORwrench…Tips, Tricks, and Info - September 2018

Posted 5 years 255 days ago ago by Scott Skola

Helicopter Maintenance Blog* 
September 2018

Well, I made it back in one piece again. If I missed a reply to anyone’s email just send me another.

A little late, but some history to start this month…

Historic Sycamore Helicopter Flies Home

The world’s last flying Bristol 171 Sycamore helicopter will return home to Weston-super-Mare this month when it flies to the Helicopter Museum; 60 years after it was built. The historic aircraft land at the museum on Monday 11 June and be based in its Duke of Edinburgh Hangar until Sunday 24 June. It will be the UK’s first Sycamore flight in 46 years. 

Sycamores have the distinction of being the first British helicopter to receive a certificate of airworthiness and also as being the first British-deigned helicopter to serve with the Royal Air Force. The aircraft were built by the Bristol Aeroplane Company, firstly at its Filton factory and then from 1955-59 at its Oldmixon factory after all helicopter design and manufacturing was moved to Weston-super-Mare.

Bristol 171 Sycamore XG545/OE-XSY is now the only airworthy example in the world and made its first flight from the historic Weston Airfield on the 3 February 1958, before being delivered to the West German Navy in VIP configuration and later transferring to the German Air Force. 

After retirement the aircraft, now privately owned, was moved to Switzerland where it was repainted in RAF colours in 1988 and then eventually sold to the Flying Bulls display team based in Austria 18 years later. By this time the aircraft required an extensive overhaul and with technical assistance from the Helicopter Museum, including the supply of archived maintenance manuals, the Sycamore flew again in July 2013.

When the aircraft arrives at the museum it will be over 60 years since it left Weston-super-Mare for Germany and incredibly the first Sycamore flight in the UK since 1972. It is visiting the UK to appear as a grounded, static display at several air shows, but its arrival at the museum will be a once in a lifetime opportunity to see the aircraft actually in flight. 

The Helicopter Museum is home to the world’s largest collection of rotorcraft including two other Bristol Sycamores, one of which (XL829) was the last to be delivered to the RAF.   

Note to Editors: The museum is currently awaiting an ETA for Monday 11 June. 

If you require any further information or would like to visit the Helicopter Museum to cover the Sycamore’s arrival please contact Peter Michallat via [email protected] or 01934 625227. 

ATA 57 
Main Rotor
Airbus (Sud Aviation)
SA315B Lama/SA316B Alouette III

Today, let’s discuss the legendary after-market fiberglass main rotor blades for the Lama/Alouette III, referred to as ‘”LOM” blades. They were developed by the LOM Corp for RMH Development in 1984. 

Their introduction caused somewhat of a stir, because at that time the factory aluminum-skinned 11.30 blades had a 4500 hour Service Life, and the LOMs came out with a 6000 hour life limit, at a similar cost. 

The helicopter manufacturer did not appreciate that the FAA had approved these blades for their helicopter without consulting them, not to mention the longer Service Life would erode their blade sales. Also the composite blades were more efficient and increased the lift capability of the helicopter by 190 lbs., and they were individually replaceable. The helicopter manufacturer hated them.

It should be mentioned here also that the factory blades at that time were supplied as indissociable, or matched sets, and could not be replaced individually. If you needed to replace a blade, the factory must match the replacement to your other two blades, by flying them in on a tower at the manufacturer’s European base and issuing a log card identifying the two blades it is mated to.

This could take months, so some US operators mixed blades from these sets and tried to bring them into harmony with a Chadwick balance device. The Chadwick at the time lacked the capability to analyze chord-wise balance--only span-wise—so the results were unsatisfactory.    

Rumors circulated that the LOM blades had a flight phenomenon, but it took several years for the blade manufacturer to nail it down. At high, heavy, fast, and cold conditions, the blades could induce violent feedback in the main rotor controls and cause the pilot to find religion. 

I inspected an Alouette III that had landed outside Evanston, WY after experiencing the phenomenon in the winter of 1987 with full passengers. I can still recall the look on the pilot’s face. The blade manufacturer’s 1990 Service Information Letter #1 says that the phenomenon affects Alouette IIIs, not Lamas, and that the mitigation was to reduce collective.

So everyone was angry. The helicopter manufacturer felt that they should not be held liable for their helicopters not equipped with their blades, blades which they did not approve of, and furthermore they felt the blades might be causing parts to fail. 

Thereafter, the helicopter manufacturer included a last question on their application for component TBO extensions:  “Has this helicopter ever had LOM blades installed?” If you answered yes, you might not get the request granted, unless the necessity for the TBO extension was due to the manufacturer’s lack of timely parts support for overhaul. 

On the maintenance side, an inspection is recommended by the LOM blade manufacturer after flight in extremely heavy turbulence by sending the blades in for inspection by them. No reference is made to any corresponding airframe related inspections. One has to reasonably conclude that the helicopter manufacturer’s “Inspection after Flight in High Turbulence” would suffice, but it only deals with the factory main rotor blades and the horizontal stabilizer. 

After extreme turbulence, vibration, or ground resonance, a Lama or Alouette should be exposed to a detailed inspection, especially of the flight controls, the lower mixing unit, and upper bellcrank.
[Submitted by the Lama-Nator*]

* For those who would like to contact the Lama-Nator directly: [email protected]

A couple FAA SAIBs on Agusta/Leonardo transmission plates and HEC ops:


Have an old tip or trick you’d like to share with your fellow mechanics? Or maybe a question that you can’t seem to find an answer to? Or just some info to pass on?  Send an email to: [email protected]

About the author: After 32 years maintaining helicopters in various capacities, Scott concluded a full time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line tinkering on aircraft for beer money. 

*To keep the hounds at bay, the information contained in this blog is for discussion purposes only.