cypres and helicopter jumps

[mr2mk1g 10]

Here's a question for you to ponder.

Ya' know how the cypres manual states it's a big no-no to descend in the plane below the altitude of your landing field...

Well I recently had the pleasure of doing a whole load of helicopter jumps and during take-off my Suunto usually read about -75ft due to the ground effect of a really big helicopter getting its ass and 20 odd people airborne.

Do you think this will have an effect on the cypres?

[IanHarrop 42]

I would not be concerned unless you were also descending at over 78 mph at the same time

"Where troubles melt like lemon drops, away above the chimney tops, that's where you'll find me" Dorothy

[riggerrob 643]

Cypres does not arm itself until you climb above 1500 feet.

[kelpdiver 2]

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Ya' know how the cypres manual states it's a big no-no to descend in the plane below the altitude of your landing field...

I thought the Cypres manual had specified a certain max negative altitude, but it just says don't.

75ft isn't a lot in terms of pressure. I believe the unit keeps sampling pressure during the day and might view the helicopter as a increase due to weather variation. If so, then it is going to fire slightly lower.

[MrBrant 0]

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Cypres does not arm itself until you climb above 1500 feet.

I'm guessing (completly and utterly) that they're worried about the cypres re-calibrating itself to below DZ level, then not firing in time? that doesn't have anythign to do with the arming does it?
or am I way off base here?

[pchapman 279]

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during take-off my Suunto usually read about -75ft (...)
Do you think this will have an effect on the cypres?

The first two replies to this post are insufficient to make a decision. I can clarify something about the point the original author is trying to make, and to note a possible source of confusion, but I can't provide a definitive answer.

The original author must be referring to the rule that one must not descend below the elevation of the takeoff or landing airfields, as stated in the Cypres 1 & 2 User's Guides.

The manual doesn't state what to do if the aircraft does go lower. All I remember hearing is that the Cypres may recalibrate, believing that the ground level is at -75 ft in this case.

What to do? One can't know what the Cypres is thinking, whether the short time "below zero feet" was sufficient for it to recalibrate or not!

None of the options are perfect:
- turn off Cypres
- accept a possibly 75 ft lower Cypres activation altitude
- fly at almost ground level, and when the Suunto or other precision altimeter shows a steady nearly zero feet, turn the Cypres off and on to recalibrate it at that level. I bet few would want to try this, and anyway the manual says not to turn on the Cypres inside a flying aircraft.

There's also some confusion in Cypres documentation about the descending-below-takeoff rule vs. the 1500 ft arming rule.

The text in Cypres documents say to avoid descending below takeoff or landing elevations.

(Eg, Cypres 1 User's Manual section 7, Cypres 2 User's Manual section 8, Jump Pilot brochure on Airtec web site.)

(There's actually more detail than that -- It gets messier if one deals with different takeoff and landing elevations. Some of the statements made by Airtec is slightly contradictory if applying formal logic, but are still understandable in real terms.)

The diagrams that accompany the text differ slightly. The Cypres 1 manual does not show 1500 ft anywhere, but the Cypres 2 manual and Jump Pilot brochure do: The prohibited flight profiles includes a climb to 1500 feet before making dips down below different possible landing elevations.

That makes it confusing: Is it only prohibited to descend below takeoff & landing if one has already gone past 1500 ft to arm the Cypres? If so, the diagram contradicts the text. I'd like to hear an explanation of this. But without further information, I'll assume that the both the texts' and diagrams' prohibitions apply. Therefore I bet the broader prohibition of the text does apply -- The prohibition on descending below takeoff & landing applies whether or not one has already crossed the 1500 ft mark.

Has Airtec or SSK been asked about all this?

While the manual does mention the special case of pressurized aircaft, I've never heard of this large helicopter pressure issue before.

[mr2mk1g 10]

That was pretty much my take on the question.

Maybe I'll get round to e-mailing airtec about it. For me it's a point of academic curiosity... for others who make use of these fantastic jump ships regularly it might actually be worth knowing about.

[DancingFlame 0]

Hi, Matthew.
We had some (3-4) cypres fires and 2 Vigil fires at Kolomna on Mi-8 loads. Everything was OK. Seems like ground effect from helicopter-made airstrem does not confuse electronic devices (like Pro-Track and Cypres).

[mr2mk1g 10]

Well seeing as that was precisely the place and aircraft on which I experienced this effect, that's good evidence.

I'd still be curious to see if the cypres fired 75ft lower than expected though... perhaps thinking the ground had been reset lower... then again logic would suggest it would take more than a simple momentary change to adjust ground level.

[DancingFlame 0]

Well in that case Pro-Track should beep 75 ft lower than usual when helicopter is climbing. But it beeps precisely at 300 meters. Cypres seems to have similiar logic.