inadvertant long line release

chopper1960 · June 3, 2013

Earlier this year I had an inadvertant long ling release. I don't know what happened but interestingly enough I had just flown past two large microwave towers 10 seconds prior!. I have been doing some research and it seems there has been some mention of utlizing shielded long lines to protect against E.M.I. ( electromagnetic interferance) One referance is from San Dimas Tech and development center in which they state that class C loads ( Non Human ) be protected for up to strength of 20 volts per meter?

They also say Class D ( human) loads be protected up to 200 volts per meter?

No one I talk to has any idea where this info comes from and where the referance for these numbers come from.

If any one has any information or therory regarding this topic I would really appreciate thier input.

Regards Chris Porter.

iChris · June 4, 2013

Earlier this year I had an inadvertant long ling release. I don't know what happened but interestingly enough I had just flown past two large microwave towers 10 seconds prior!. I have been doing some research and it seems there has been some mention of utlizing shielded long lines to protect against E.M.I. ( electromagnetic interferance)

One referance is from San Dimas Tech and development center in which they state that class C loads ( Non Human ) be protected for up to strength of 20 volts per meter?
They also say Class D ( human) loads be protected up to 200 volts per meter?

No one I talk to has any idea where this info comes from and where the referance for these numbers come from.
If any one has any information or therory regarding this topic I would really appreciate thier input.
Regards Chris Porter.

Those were proposed rules for FAR 27.865 and FAR 29.865 (external load attaching means) that went into effect October 1999 (Amdt. 27-36); therefore, if your helicopter and/or cargo hook came off the assembly line prior to that date, it was the option of the manufacturer to take such protective measures.

You should ensure your electrical release cable is shielded and that shield is at ground potential. The cargo hook assembly should also be at ground potential.

Proposed Amendments to Sects. 27.865[3][ii] and 29.865[3][ii]

Proposed Sacts. 27.865[3][ii] and 29.865[3][ii] would require protection of the quick-release subsystems against potential internal and external sources of electromagnetic interference (EMI) and lightning. The new requirements are necessary to prevent inadvertent jettison of NHEC and HEC from sources such as stray electromagnetic signals, static electricity, and lightning strikes. Proposed field intensity levels are 200 volts per meter for applicable portions of QRS used for HEC and 20 volts per meter for applicable portions of QRS used for NHEC. The purpose of the requirements is for those applicable portions of the QRS to withstand these field intensity levels without inadvertent load release.

Notice of Proposed Rulemaking. Notice No. 98-6; Issued on 07/06/98.

The highest percentage of these inadvertent release or mechanical

Edited June 4, 2013 by iChris

500F · June 5, 2013

IChris,

It is still the option of the hook manufacturer to take such measures. To date, no single hook has been able to comply with those measures (not the voltage requirement spicifically, but the HEC requirements of 27.865 in general) and therefore the hook manufacturer must have Class B (HEC) not permitted printed in the flight manual suppliment. Any hook made before October 1999 had no such requirement or testing done in its certification and therefore has no such language.

As Chris said, the majority of inadvertant releases are due to a misrigged or broken manual release cable. Also a relatively common cause is roll out on keeper style cargo hooks with a improper ring utilized. The next most common is pilot inadvertant release. Electrical interference is few and far between and as far as I know (and as far the forrest service knows), has never been conclusivly proved to have caused a release. Given the guys that work on energized 500kv lines with the hooks (no special insulation) never have issues I'd say the chances of it having been electrical are slim to none. Check out your manual release cable and rigging.

chopper1960 · June 10, 2013

As you say there has never been any known or proven accounts of this happening. I myself work around 115k v 230kv and 500kv.lines almost daily and have delivered 100's if not 1000's of these loads since I started at my job with ontario's provincial hydro electric company. I have not had such an issue and neither have any of my co-workers.

With more background on this the a/c was sent back to mfg. for maintenance check as well as on site engineer went through system. The long line was inspected locally and sent back to mfg. for inspection. All findings were that there were no abnormalities with heli or Line.

It has been written up as pilot error! The only problem is this pilot knows he did not hit the button.

In Canada we do not even have to report inadvertant releases to transport unless there is someone hurt or put in harms way. I am not sure what the reporting protocol is in the us but if they are not reported and conditions not recorded how do we know if this is actually not an issue?

I am not very good at posting web sites and info but for a few check WWW.caa.co .uk Cap426

Helicopter external load operations paragraph 2 last sentence they talk about possible inadvertant releases due to static and Radio hazards??

Also check out Aviation vortex 3/2002 it also has possible E.M.I. inadvertant release.

I do believe that part of the problem is this get put down as pilot error and are forgotten. I by no means say this is what caused the malfunction but would like to find out who did the testing and gave the requirements for the above long line specs as there had to be some research to come to these findings.

Thanks again for the comments and interest. Chris P.

500F · June 10, 2013

As I understand it the EMI shielding requirement in 278.865 is a carryover from the sheilding found on fly-by wire aircraft. The requirement refers to the hook wiring, not longline shielding.

I'm not electrician, but I dont think you are going to induce the several amps needed to open the solenoid insuch a short run of wire. If it were more complex circuit with a relay in the hook possibly. But on the standard 2 wire system I dont see it heppening.

Do you use steel longlines? If you use Dyneema it is very di-electric. If it is clean and dry it passes the test to be used as a hot rope.

In the US it would not be reportable either.

I assume this was on one of your Astars? what type of hook?