Static port blocked. BREAK THE VSI?

Rebel Lord

Rebel Lord

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Rebel Lord
So I'm reading some interesting things in my Instrument Pilot manual. If your static port is blocked you apparently can break the glass on the VSI to open an alternate state port.

Anyone ever done this?
 
Rebel Lord said:
So I'm reading some interesting things in my Instrument Pilot manual. If your static port is blocked you apparently can break the glass on the VSI to open an alternate state port.

Anyone ever done this?
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I have not done this personally but am familiar with it. If the airplane does not have an alternate static source, your best bet is to break the glass on the VSI, not only should this solve your problem (with a slight error, the same as with an alternate source vented inside the cabin due to the slightly lower pressure), but a VSI is NOT a required instrument for IFR flight...kind of convenient. Got asked on my IR check ride about an alternate source during the oral, he said, "Does the plane we are flying today have an alternate source?" I said nope, but I can break the glass on the VSI. He had no objection to this.
 
I learned this in primary training. We just simulated it though, never broke the VSI glass in our plane to try it.

In real life, VFR at least, i'd be loathe to do it, vs just landing without the altimeter and using my eyes to get me on the ground at the airport, bs fussing with finding something hard enough to break it, breaking it, knowing the readings are off, but trying to remember which way, and then trying to land
 
MIFlyer said:
I learned this in primary training. We just simulated it though, never broke the VSI glass in our plane to try it.

In real life, VFR at least, i'd be loathe to do it, vs just landing without the altimeter and using my eyes to get me on the ground at the airport, bs fussing with finding something hard enough to break it, breaking it, knowing the readings are off, but trying to remember which way, and then trying to land
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With a blocked static port you would also lose your airspeed indicator which I would consider a bigger issue.
 
Hopefully you'd have a maglite or similar in your flight bag. Otherwise I don't know how you'd break it.
 
MassPilot said:
With a blocked static port you would also lose your airspeed indicator which I would consider a bigger issue.
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Hopefully you've done practice landings with an instructor simulating a ASI. If not, it's a good exercise to do. It's not uncommon for bugs, birds, pilot tubing failure, etc., to cause the airspeed indicator to fail, even if you have a clear static port. Fly by numbers and land by feel.
 
Brad Z said:
Hopefully you've done practice landings with an instructor simulating a ASI. If not, it's a good exercise to do. It's not uncommon for bugs, birds, pilot tubing failure, etc., to cause the airspeed indicator to fail, even if you have a clear static port. Fly by numbers and land by feel.
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Oh I have, and I once took off with the pitot tube cover on (ASI came alive but was inaccurate) and had to do it for real. My point was that given the choice between an ASI failure and an altimeter failure, I would take the altimeter failure.
 
Rebel Lord said:
So I'm reading some interesting things in my Instrument Pilot manual. If your static port is blocked you apparently can break the glass on the VSI to open an alternate state port.

Anyone ever done this?
Click to expand...
1) Use alternate static port. Most IFR equipped airplanes have a means of acquiring alternate static pressure. Otherwise,
--If VFR, just keep flying and land at first practicable airport
-- If IFR, break glass, use GPS assistance, report to ATC failed instrument. Know your systems. Does your GPS use a separate source for static pressure? How far are you from VFR weather?
 
I fly a G1000 C172. If I had a blocked static port could I break the standby ASI or altimeter to get the PFD pitot-static instruments working (assuming the alt static port was blocked too)? I'm just curious.
 
Noted and I will remember it for that situation down the road where all three of my static ports are blocked while I'm in hard IMC. Great tip!
 
MassPilot said:
I fly a G1000 C172. If I had a blocked static port could I break the standby ASI or altimeter to get the PFD pitot-static instruments working (assuming the alt static port was blocked too)? I'm just curious.
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The input to the alternate static is inside the plane, so if that is blocked, you have really big issues :cool:
 
MassPilot said:
With a blocked static port you would also lose your airspeed indicator which I would consider a bigger issue.
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d'oh!!! thanks for the reminder, yes, that's a lot more important, I would grab the mini-mag to break the VSI glass if for some reason the alternate air didn't work
 
I've seen tape left on one of the static ports after altimeter check. The aircraft has 2 external ports so I just assumed the tech took the tape off of one and forgot about the other. Something to keep in mind when preflighting an aircraft after it has had an altimeter check.

I have heard of a guy who didn't check the static port and didn't recognize the source of a problem with altitude reporting. Supposedly a shop sold him a new transponder and found the tape over the static port when they installed the transponder. The guy was goofy enough and the aircraft in bad enough shape that I tend to believe the story.
 
MassPilot said:
Oh I have, and I once took off with the pitot tube cover on (ASI came alive but was inaccurate) and had to do it for real. My point was that given the choice between an ASI failure and an altimeter failure, I would take the altimeter failure.
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In IMC, I would reverse that. You can fake airspeed by the numbers, partial panel. Altitude comes from nothing else. And it sucks to hit obstructions or terrain because you don't know how high you are.
 
MAKG1 said:
In IMC, I would reverse that. You can fake airspeed by the numbers, partial panel. Altitude comes from nothing else. And it sucks to hit obstructions or terrain because you don't know how high you are.
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Fair enough. I'm not instrument rated and I've never been in IMC.
 
DGlaeser said:
The input to the alternate static is inside the plane, so if that is blocked, you have really big issues :cool:
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Oh I know. I was just curious as to whether there is some special property about the VSI that when broken can create a new static port or if any of the pitot-static instruments can do it.
 
MassPilot said:
Oh I know. I was just curious as to whether there is some special property about the VSI that when broken can create a new static port or if any of the pitot-static instruments can do it.
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Any(IIRC), but it's the least important instrument.
 
MassPilot said:
Oh I know. I was just curious as to whether there is some special property about the VSI that when broken can create a new static port or if any of the pitot-static instruments can do it.
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It is just a matter of opening up the static system to atmospheric air again so you can get a reading. Breaking the VSI accomplishes that and it is the least important static instrument. In most IFR planes it would be very rare to get to that point. Mine has 2 exterior static ports, as well as an emergency port under the panel.

The correction is that cabin pressure is slightly lower than outside pressure. So altimeter will read high, airspeed will read high, and VSI will show a climb for a second. The difference is negligible from a practical sense.

Sent from my SM-G920V using Tapatalk
 
GeorgeC said:
I tried that on the PFD but it just made the problem worse.
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MassPilot said:
Oh I know. I was just curious as to whether there is some special property about the VSI that when broken can create a new static port or if any of the pitot-static instruments can do it.
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Any of the instruments hooked to the static system would likely suffice. The reason the VSI is recommended is because it is the least necessary for instrument flight and it is not required equipment (per the FARs anyway).
 
I seem to recall that if one does that, there is some adjustment to make because the pressure INSIDE the cockpit is not the same as outside? Am I dreaming? Right now I am thinking it must be the same as they position the static port to be least affected by dynamic air streams. On the other hand, it is outside so air is rushing past it.

I'm sure I read that, and I think it was in the Piper manual which has an alternate static port but one that is inside, and there was a caution. I'll have to check.

Oops...I didn't see drottos' post. Thanks! I wasn't forgetting (though I did forget which way it would affect it)
 
LongRoadBob said:
I seem to recall that if one does that, there is some adjustment to make because the pressure INSIDE the cockpit is not the same as outside? Am I dreaming? Right now I am thinking it must be the same as they position the static port to be least affected by dynamic air streams. On the other hand, it is outside so air is rushing past it.

I'm sure I read that, and I think it was in the Piper manual which has an alternate static port but one that is inside, and there was a caution. I'll have to check.

Oops...I didn't see drottos' post. Thanks! I wasn't forgetting (though I did forget which way it would affect it)
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Just remember that the error generally make you less safe: it makes you think you are higher than you are, and it makes you think you are going faster than you are.
 
Another option that doesn't involve actually breaking things: if you know your airplane well, and you know where your altitude encoder is located, reach under and yank the static line off of it. Most are just pushed on and nothing is going to break when you remove it. After the flight your shop can just stick it back on. In my Viking, the encoder is just above my right knee, so it'd be much easier to reach under, find the line and pull it free than to try to break an instrument face. Much tougher in my twin, but if I had a passenger I could have them reach under the panel and take care of it. This, of course, assumes you're pretty familiar with how the back of your panel is setup. Practical in some airplane, probably impossible in others.
 
I guess that explains the lack of glass in the VSI faces in the rental fleet I used to do my instrument training with.
 
MassPilot said:
With a blocked static port you would also lose your airspeed indicator which I would consider a bigger issue.
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??? Perhaps a bit inacuraate, but you wouldn't lose it. At low altitudes I would think the correction is manageable.

Breaking the VSI is a solution from many years ago. Just know the errors, including a lag in altimeter.
 
Kritchlow said:
??? Perhaps a bit inacuraate, but you wouldn't lose it. At low altitudes I would think the correction is manageable.

Breaking the VSI is a solution from many years ago. Just know the errors, including a lag in altimeter.
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With a blocked static port your ASI is going to read accurately at the altitude it blocked, slow if you climb, and fast if you descend.

Thus the biggest issue is if it blocks at high altitude, and as you eventually must do, you have a large descent it become completely inaccurate on the dangerous side.

Sent from my SM-G920V using Tapatalk
 
drotto said:
With a blocked static port your ASI is going to read accurately at the altitude it blocked, slow if you climb, and fast if you descend.

Thus the biggest issue is if it blocks at high altitude, and as you eventually must do, you have a large descent it become completely inaccurate on the dangerous side.

Sent from my SM-G920V using Tapatalk
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I agree it will become inaccurate, but I do think managing the inaccuracy is very possible.
 
I've flown a plane with blocked static twice. The first time I knew about it in advance and it was an Arrow with an alternate static valve in the cockpit. We flew around doing some tests (working the drains, etc...). On the way into the maintenance shop I shut the alternate static on approach. We taxied up to the shop and parked with the ASI reading 50 knots.

The second time was in the Navion. It was the day after 9/11 that they allowed me to "evacuate" from VKX. I knew something as I'm climbing out and the altimeter isn't rising very fast. I told ATC and they essentially said "stop altitude squawk and get out of the airspace." The only trick was wondering if I was below Vle on approach. I just used the GPS groundspeed coupled with the ATIS winds to guess at it.

So I'll disagree with Kritchlow. In both times, the ASI was pretty much "unmanageable." Fortunately, I was familiar with both planes to fly them without a reliable ASI.
 
drotto said:
With a blocked static port your ASI is going to read accurately at the altitude it blocked, slow if you climb, and fast if you descend.

Thus the biggest issue is if it blocks at high altitude, and as you eventually must do, you have a large descent it become completely inaccurate on the dangerous side.

Sent from my SM-G920V using Tapatalk
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Why would it be large? You still have static air (delayed) reaching the ASI.

Assumption: You are not flyng a pressurized airplane.
 
flyingron said:
I've flown a plane with blocked static twice. The first time I knew about it in advance and it was an Arrow with an alternate static valve in the cockpit. We flew around doing some tests (working the drains, etc...). On the way into the maintenance shop I shut the alternate static on approach. We taxied up to the shop and parked with the ASI reading 50 knots.

The second time was in the Navion. It was the day after 9/11 that they allowed me to "evacuate" from VKX. I knew something as I'm climbing out and the altimeter isn't rising very fast. I told ATC and they essentially said "stop altitude squawk and get out of the airspace." The only trick was wondering if I was below Vle on approach. I just used the GPS groundspeed coupled with the ATIS winds to guess at it.

So I'll disagree with Kritchlow. In both times, the ASI was pretty much "unmanageable." Fortunately, I was familiar with both planes to fly them without a reliable ASI.
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Okay, I think I see the miscommunication here.
My premise is a blocked Static port with a broken VSI glass.
 
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