Wondering what percentage of 139's have glass or heated glass windshields? We do have plain glass and have busted 4 each ( 1 RH, then 2 LH and just now the second RH) in the space of 14 months and 103 flt hours.
PPG says FOD impact, but we only go airport taxiway to airport taxiway 99.99% of the time. Always hangared. Anyone with glass seen any micro chipping or such and not had window shatter.
PPG says that the specification for airworthiness is 10% damage depth and still OK, ie 0.012" is limit for damage on each layer of 0.125 glass. I measured our last FOD crush mark and got around 0.007", but optical micrometer will get more accurate data when returned to PPG.
Fly to Philly tomorrow to let AW investigate and determine if we have a freak airframe with a weird frequency or vibe and/or flexing nose section. Owner will not fly in again until cause is found.
Anyone got any info on glass windshield reliability, care to respond.
There was an issue with ppg glass windows on Bell mediums a little while ago, our fleet had three or 4 new ppg glass windshields crack, two cracked with the aircraft just sitting on the ground.
I believe it came down to a run of mis-formed windows, they were not contoured to match the airframe and when installed were put under constant stress.
I would check to see that the windshields fit properly when installing the next ones.
Oh yeah, we are down on shimming and trimming and radiusing inside edges after 4 of these. Third window (2nd LH) took 3 attempts to get a window that didn't arrive with defects or would actually fit in airframe contour of opening without rocking from corner to corner.
Coincidentally our first one happened in our hangar overnight too. That has the "experts" stumped
I've done a couple of glass windscreen installs and they fitted perfect.
No trimming, all holes lined up perfect, no shimming required, fitted the curvature of the airframe perfectly.
Both plastic screens off and glass on and sealed in 8 hours.
They have been on for more than 3 years with no issues and I've seen a 5 year old machine still with original glass windscreens with no issues or damage.
A bad batch perhaps?
I have only fitted them to AW machines, not Philly machines. Having accepted machines from both factories, I would have to say the Italians put out a better product. Hard to believe I know!
We have 3, 2 with heated glass screens the other is plastic. we have had 1 screen failure LH at around 15 hours (Italian machine). No problems since and around 1200 hours. The heated screen inverters Keep failing must have had 3 or 4 now. Pain as they are under the cabin floor.
Yeah, unlucky is one way of putting it! Our ship is an Italian built one from Oct 2006. The original windscreens lasted 5 years and approx 350 hours. Next two have lasted 25 and 103 hours over 14 months. Serial numbers start with the year and have been 08, 10, 11 and now 12. A couple of replacements that arrived were U/S due to possible cracking in edge and one that rocked from either corner to corner in opening and a worst gap originally of 0.125?. Last replacement of LH window was done at annual insp due to one of the earlier replacements having a 2" band of distortion along the bottom edge and took 5 hours to have out and replaced. My opinion of PPG QA is pretty average at the moment.
Interested to know if anyone is flying around with glass that has minor pitting from FOD or ?? and if so is it just 1 or 2 impact/crush points or is it numerous.
As I implied we are not flying out of a gravel pit in East B*mfu*k and can't recall where we might have picked up so many FOD impacts, unless it's those stuffy corporate jets at the airports we go to throwing up sand in our face!
Last edited by KiwiRotorWrench; 25th Aug 2012 at 23:43.
EASA CS29 and FAA FAR-29 regulations require that:
Quote:
The aircraft is able to continue safe flight and landing (Cat A) or safe landing
(Cat B) following impact with a single 1kg bird at the greater of the maximum safe airspeed (VNE) or maximum level-flight airspeed at rated power (VH) (at up to 8,000 ft).
How do these windshields manage to pass that requirement and crack while sitting on the ground? I recognize that there is a difference between a crack and having a 2lb bird go right through the laminated sections of glass but come on.
The Aussie MRH90 has been going through lots of windscreens. NHI (with AW in there somewhere) say it is probably FOD related - the composite airframe transmits much more stress to the windscreen, then any small chip or thermal imbalance can set up a crack mechanism. Might be the same for 139. NHI fix is to mount windscreen with more flexible "glue", have slightly larger locating holes, and fit a clear film on the outside. The film has been trialled and works really well.
I was hoping to get some help solving this mystery. I have had the same results on 3 separate aircraft.
When plugged in to the single cabin ICS panel and trying to speak over the cabin PA system there is this constant overbearing squealing feedback which renders the message all but unreadable. I have followed the instructions in the manuals and every possible variation of settings on the control panel and used different headsets.
Parasitic oscillation is an undesirable oscillation caused by feedback.The problem occurs notably in audio and other electronic amplifiers. Parasitic oscillation is undesirable for several reasons. The oscillations may radiate from the circuit, causing interference to other devices. The oscillations waste power and may cause undesirable heating. For example, an audio power amplifier that goes into parasitic oscillation may generate enough power to damage connected speakers. A circuit that is oscillating will not amplify linearly, so desired signals passing through the stage will be distorted. In digital circuits, parasitic oscillations may only occur on particular logic transitions and may result in erratic operation of subsequent stages; for example, a counter stage may see many spurious pulses and count erratically.
If you insist to speak from inside PAX area you need one extra piece of electronic kind of phase inverter in line after your mike, or you need to manually reduce volume on PA on appropriate level before parasite oscillation starts. Tip: Go and talk from cockpit....
We have quite a few of these ships in our fleet and they are all configured similarly with the single cabin comm panel. I will look into that modulation adjustment on the mics and we may have to set aside a kit for "cabin only" headsets if that fixes it. There are no problems with David Clarks, or any other brand, on our standard 139 cockpit avionics systems.
@9Aplus I think we've all experienced normal feedback from a speaker to a microphone, and thats what I tried to compensate for by trying "every possible variation of the settings" as I said. Oh, and thanks for the tip but its not me who insists on speaking from the cabin, its the customer, I'm fine doing it from my seat and the PA works great from there. If there were an additional piece of electronic phased inverter needed one would assume that the manufacturer would know this and it would be installed...
Being that Agusta sold us all these ships with this configuration, and the few I've tested are all producing the same results, we'll probably need to get their help in figuring it out. I just wanted to see if anyone has had similar experience with this particular aircraft in a similar configuration and if they found a solution.
I'm just a pilot trying to help my guys out. Thanks for the suggestions.
Most of ours are glass but I have seen at least two without. The scratches from the wipers are the biggest problem with those non-glass types from what I can see.
As for the cracking; I can't speak from experience on the AW139s but I have seen a bad batch of UH60 glass from PPG in the past. During one 45 day training exercise in the California desert we replaced around 15 (I think it was more) panels, one day after the next, both LH and RH on multiple aircraft. At first we were thinking it was caused by intense heat changes inside and out but we ruled that out, then we were afraid the install procedures/shimming was being done wrong, ruled that out as well after having a dozen or so people involved in supervising the process. Eventually chocked it up to a bad batch. We eventually got through that batch and never had problems again.
As for the pitting; Some of our S76s have glass that is so old that you can see micro pitting and scratches across the whole panel, looks as if its been on there for 20 years or more. It is not noticeable unless you really look up close though. Now that was a good batch of glass!
I picked this up from BookFace: surprised that we haven't mentioned it on Rotorheads yet? 1800 hours on the blade,
Quote:
This is what happened during our flight on the 7th of Sep 2012 on you way back from Gilgit(OPGT) to Islamabad(OPRN) on the 139. Experienced strong vibrations at 120 kts, reducing speed to 60 Kts did not help our case, hence had to force land in huripur, 10 mins short of OPRN. The first skin of the blade was pealed off. Did field repairs and changed the blade, flying back to base early next morning.
Firstly the terminology is wrong. This is a delamination, not a disbond.
My initial thoughts are that the white surface is suspicious. When composites are supplied there is a release ply on the surface so that the roll of material does not stick to itself on the roll. That release material is usually left in place until the next ply is just about to be laminated over the top of it. The release ply is then removed. If it is not removed, then there is a very high probability of delamination. I suspect that this is the case, but to be sure I would require a sample of the white material.
If this is the case, there has been a QA stuff-up in processing the laminate. Good QA practice would require checking every release ply has been removed either by visual examination prior to the next laminate being applied and/or by reconstructing all of the release plies after the lamination process.
What concerns me about these pictures is the "no disbond" notes on the areas surrounding the delamination. This is a very clear indication of how totally ineffective NDI is. It would be an absolute miracle if that release material was limited only to the delamination area. What is happening is that there is sufficient contact around the delamination between the release ply and the next layer that ultrasound (or tap testing) can not find the release material. It will be there, NDI just can not find it.
People need to understand the limitations of NDI. It can only find some defects when there is an air gap. It is a negative test, not a positive test. Passing NDI is not definite evidence of airworthiness.
AW139 Cabin PA Squealing Feedback?
