Alternate static source

[twinbird]

I'm new to Sikorsky S-76D and wondering why alternate air source is not equipped with S76D?
As far as I know the regulations in FAA is as below

AC 29 APPENDIX B. AIRWORTHINESS GUIDANCE FOR ROTORCRAFT INSTRUMENT FLIGHT
(9)IMC Evaluation.
(B) An alternate static source with a means of selecting this source must be provided for single pilot configurations.

[hueyracer]

I am not familiar with the S-76....but this one seems obvious (though i could be wrong):


(B) An alternate static source with a means of selecting this source must be provided for single pilot configurations.


S-76 Crew:
Two pilots

[Nescafe]

S-76 Crew:
Two pilots

The S76 D is certified single pilot IFR.

[Fareastdriver]

In the 1960s we were briefed to get the crash axe out and smash the glass on the altimeter. (somewhere where the needles weren't)

[Nescafe]

In the 1960s we were briefed to get the crash axe out and smash the glass on the altimeter. (somewhere where the needles weren't)

Probably not a current SOP for an S76D ;-)

[Ascend Charlie]

The 76B was SPIFR but I don't recall seeing an alternate switch. Mind you, there were 645 separate switches, knobs, dials, circuit breakers and other things to twiddle, so perhaps I missed it when I counted those things one idle morning.

[gulliBell]

The S76 D is certified single pilot IFR.
And assuming all S76D have a dual pilot instrumentation fit out, the co-pilot side which relies on a different static source to the pilot side becomes your alternate instruments. As if your aircraft was single pilot IFR, not fitted for dual pilot operation, and the primary pilot side instruments had an alternate static source switch.

[212man]

And assuming all S76D have a dual pilot instrumentation fit out, the co-pilot side which relies on a different static source to the pilot side becomes your alternate instruments. As if your aircraft was single pilot IFR, not fitted for dual pilot operation, and the primary pilot side instruments had an alternate static source switch.
Exactly my thoughts, being a glass cockpit, it has a Reconfiguration Control Panel, so if one system becomes blocked you can select the other side. Interestingly, Part 25 does not mandate it which is entirely logical when you consider that most Part 25 aircraft are pressurised, so the concept doesn't works so well! The wording of the part 25 requirements match the situation of using an RCP though:
Except as provided in paragraph (h) (https://www.law.cornell.edu/cfr/text/14/25.1325#h) of this section, if the static pressure system incorporates both a primary and an alternate static pressure source, the means for selecting one or the other source must be designed so that -

(1) When either source is selected, the other is blocked off; and

(2) Both sources cannot be blocked off simultaneously.

[Flying Bull]

Hi there,

with glas cockpit watch out for the new way of selecting alternate static source.
I´m not flying the S76 - but a modern helicopter from another manufacturer - and by now its no longer just switching a guarded switch...
You need to tell the computers that you are doing it in correct order of steps - or you f... up ;-)

Static is then taken from inside the cabin.

[RVDT]

Hmmmm. So when IMC how do you "know" when your static source is "blocked"?

Asking for a friend.

[gulliBell]

Discrepancy in altitude or rate of climb indication between co-pilot side and pilot side instruments. ASI also uses static pressure so there will be a discrepancy there as well.

[RVDT]

Discrepancy in altitude or rate of climb indication between co-pilot side and pilot side instruments. ASI also uses static pressure so there will be a discrepancy there as well.

So long as the "reason" is not common to all. Masking or insulation tape has proven effective in the past!!

[gulliBell]

Masking tape on the static ports would be revealed during the takeoff process, I would have thought. Certainly your VSI would not be showing a climb, you should catch that very early on.

[mnttech]

In the 1960s we were briefed to get the crash axe out and smash the glass on the altimeter. (somewhere where the needles weren't)
I thought it was the VSI you broke?

[SASless]

MTech,

My memory agrees with you....it was the VSI that wanted breaking.

[212man]

MTech,

My memory agrees with you....it was the VSI that wanted breaking.
yep - the least important of the pressure instruments

[212man]

Masking tape on the static ports would be revealed during the takeoff process, I would have thought. Certainly your VSI would not be showing a climb, you should catch that very early on.
more of an issue for fixed wing, as they have committed to getting airborne before any indications present themselves. AeroPeru comes to mind.

[[email protected]]

SODPUD RVDT:ok: - ASI errors = Static blocked, ASI overread in a descent - Pitot Blocked, ASI underread in a descent

[gipsymagpie]

SODPUD RVDT:ok: - ASI errors = Static blocked, ASI overread in a descent - Pitot Blocked, ASI underread in a descent

I actually had a pitot blockage once and what happened was that the airspeed drops to zero. Theres drain holes in the pitot tube sides for moisture so the pitot line effectively goes to ambient meaning the airspeed drops to zero. A bit sporting when pitch based speed hold was engaged on the AP and we nosed over!

[retoocs]

On the 76C, the static port on the pitot tube is also Tee'd to the static port on the tail cone. Does it need to be selectable if it is coming from two locations?

[megan]

Hmmmm. So when IMC how do you "know" when your static source is "blocked"?So when VMC/IMC how do you "know" when your static source has a loose connection and is reading cabin pressure? Had it in a 76 once.

[[email protected]]

Gypsymagpie - are you sure it wasn't a combined static/pitot probe? Most systems have the water drains in the plastic tubes running from the probe to the instruments/ADCs.

The SODPUD is an old mnemonic from days when separate pitot and static ports were the norm.

[ShyTorque]

I’m not qualified on the D model but I recall that the S76s I flew (A+, B, C & C+, all SPIFR) all had dual static systems, vented on each side of the tail cone, which were are heated same as the pitot system to prevent icing. I don’t recall there being a switch because in effect there was redundancy from the start.