Certified Altimeters?

[redcatcher27]

Welp. I guess you learn something new every day. I took my 1968 M20F in for an oil change, installation of a new (to me) vacuum step actuator, and 24 month IFR certification of the static, transponder, altimeter.  Mind you, I had been flying for almost three years of ownership with the old altimeter... Aircraft logs showed that it had been IFR certified roughly every 2 years since it was installed in 2004. 

Came home with a new altimeter, after I was told my old one wasn't certified for IFR flight.

They told me why they thought it wasn't, but do you know or can you guess?

BTW, the old altimeter was p/n 5934P-A56 and the new one is p/n 5934A-1.

Or maybe I just got bamboozled? Anyway, the cert along with the new altimeter cost me less than .5 AMU, so I suppose I am happy.

[Hank]

No clue on the certification, but mine looks like the bottom one. Don't think I've seen one with tick marks every 50 feet, only recall seeing the 20-foot tickmarks.

[redcatcher27]

1 minute ago, Hank said:

No clue on the certification, but mine looks like the bottom one. Don't think I've seen one with tick marks every 50 feet, only recall seeing the 20-foot tickmarks.

So, for clarity, the top one was the OLD one.  T
he bottom one, with the 20' tick marks is my NEW one.

[Hank]

Just now, redcatcher27 said:

So, for clarity, the top one was the OLD one, the bottom one, with the 20' tick marks is my NEW one.

Yes, I understood that. Never seen one with 50' tickmarks. Surely that's not what they didn't like? I would suspect something internal to the unit that's not visible from the left seat.

[redcatcher27]

No, that's it!  That's what they indicated to me - that I needed one with 20 foot tick marks! But perhaps there's an internal issue too? I don't know.

[hammdo]

I think part of the issue has to do with the 75' requirement for altimeter accuracy in IFR use. 20' increments make it easier to comply with the rules vs 50'. That is probably why... 

-Don 

[Floyd]

The Air Force E3 aircraft I used to fly had 50 ft marks.  Flew alot of IFR.

[Hank]

5 hours ago, Floyd said:

The Air Force E3 aircraft I used to fly had 50 ft marks.  Flew alot of IFR.

U.S. military aircraft are not certified by the FAA, and pilots have the option of obtaining FAA pilot certificates.

[jamesm]

yeah you certainly don't want to get  the line for the  vacuum step confused with  static line on  the airspeed  indicator... oops .... I know a guy  who did that ....  I had never seen the air speed wind up that fast  :-O ....  I  knew immediately  what happen  the poor air speed indicator   it wound up so quickly. I can tell you that after that  experience, I can tell you that l paid  closer attention  on the   detail to my labeling  techniques and  vacuum line to step had label after that..

 

[drapo]

From what I understand, you need a «sensitive altimeter» and that is the definition: Sensitive altimeters have a 100-foot scale (20-foot tick marks) as their most precise display.

 

In Canada, there was a study done and they issued the following rule, but I'm not sure if it is interpreted the same way in the US, but usually, there are not such dramatic differences between our regulations:

The intent of the Transport Canada Aviation (TCA) policy promulgated in the November 24, 1981 memo from Headquarters to the Regions on aircraft altimeter markings and in APL No. 2 is still valid and is specified below. The following criteria defines Transport Canada requirements for altitude increment markings for sensitive altimeters:

1. For all operations to Category II limits or lower, altimeters shall be marked in altitude increments not to exceed 20-feet; and
2. For all VFR operations, which require a sensitive altimeter and all IFR operations to Category I limits, altimeters shall be marked in altitude increments not exceeding 50-feet.

 

[redcatcher27]

Great explaination! Thanks so much.

[carusoam]

Funny thing is...

I was familiar with the rules... displaying 20’ accuracy... for use in IFR...

I Know my O complies with that rule as well....

But, the 50’ altimeter markings sure look familiar... probably what my 65 M20C had...
 

What is the purpose of the hashed lines opposite of the 10k’ pointer?  (Just to show where the pointer is in the case it gets hidden?)
 

Why is one wider than the other?

Best regards,

-a-

[redcatcher27]

I think that manufacturers added the hashed lines to highlight that the aircraft is at a low altitude, in a way that's much easier and quicker for the pilot than 'parsing' multiple hands on the altimeter face. Different widths - the hashed area gets bigger as you get lower.

[HRM]

 This one has been thru many an IFR cert...what was that shops name? Don't want to go there.

[redcatcher27]

53 minutes ago, HRM said:

 This one has been thru many an IFR cert...what was that shops name? Don't want to go there.

I'd rather not say here, but if you pm me, I'll be glad to tell you.

[PT20J]

From the Instrument Flying Handbook glossary:

Sensitive altimeter. A form of multipointer pneumatic altimeter with an adjustable barometric scale that allows the reference pressure to be set to any desired level.

Cessna used to use sensitive altimeters with 50’ markings. They were certified IFR. 

When a shop tells you that you have to change a part because it’s not legal, it’s always a good idea to ask them to show you the reg. Sometimes mechanics are wrong. Sometimes pilots are unaware of a rule change. Either way, everyone learns something.

Skip

[EricJ]

A DPE I've known most of my life has a 1960 C210A that she has owned for more than fifty years.   Her husband was a PanAm 747 captain and had been an F-104 pilot in the Air Force.   Somewhere along the way he snagged an airspeed indicator from an F-104 and they put it in the 210.   It was in there since I first saw it in the mid-1970s and I always thought it was pretty cool.    They had the red line (Vne) tape on the glass as required.

I talked to her for the first time in a while a year or so ago and she was fuming mad because an IA made her take that airspeed indicator out and put one in that had all of the proper arcs marked.

So, yeah, there can be differences in opinions.   I think the red line was all that was required, but I haven't looked it up.

[N201MKTurbo]

3 hours ago, EricJ said:

A DPE I've known most of my life has a 1960 C210A that she has owned for more than fifty years.   Her husband was a PanAm 747 captain and had been an F-104 pilot in the Air Force.   Somewhere along the way he snagged an airspeed indicator from an F-104 and they put it in the 210.   It was in there since I first saw it in the mid-1970s and I always thought it was pretty cool.    They had the red line (Vne) tape on the glass as required.

I talked to her for the first time in a while a year or so ago and she was fuming mad because an IA made her take that airspeed indicator out and put one in that had all of the proper arcs marked.

So, yeah, there can be differences in opinions.   I think the red line was all that was required, but I haven't looked it up.

The TCDS probably mandates all the arcs.

[N201MKTurbo]

The TCSD specifies the airspeed indicator must be marked according to CAR 3-756. As you can see, marking the glass is allowed.

 

§ 3.756 Instrument markings.  The instruments listed in §§ 3.757-3.761 shall have the following limitations marked thereon.  When these markings are placed on the cover glass of the instrument, adequate provision shall be made to maintain the correct alignment of the glass cover with the face of the dial.  All arcs and lines shall be of sufficient width and so located as to be clearly and easily visible to the pilot. § 3.757 Air-speed indicator.  (a)  True indicated air speed shall be used: (1) The never-exceed speed, Vne—a radial red line (see § 3.739). (2) The caution range—a yellow arc extending from the red line in (1) above to the upper limit of the green arc specified in (3) below. (3) The normal operating range—a green arc with the lower limit at Vs1, as determined in § 3.82 with maximum weight, landing gear and wing flaps retracted, and the upper limit at the maximum structural cruising speed established in § 3.740. (4) The flap operating range—a white arc with the lower limit at Vso as determined in § 3.82 at the maximum weight, and the upper limit at the flaps-extended speed in § 3.742.

[EricJ]

Just now, N201MKTurbo said:

The TCSD specifies the airspeed indicator must be marked according to CAR 3-756. As you can see, marking the glass is allowed.

 

§ 3.756 Instrument markings.  The instruments listed in §§ 3.757-3.761 shall have the following limitations marked thereon.  When these markings are placed on the cover glass of the instrument, adequate provision shall be made to maintain the correct alignment of the glass cover with the face of the dial.  All arcs and lines shall be of sufficient width and so located as to be clearly and easily visible to the pilot. § 3.757 Air-speed indicator.  (a)  True indicated air speed shall be used: (1) The never-exceed speed, Vne—a radial red line (see § 3.739). (2) The caution range—a yellow arc extending from the red line in (1) above to the upper limit of the green arc specified in (3) below. (3) The normal operating range—a green arc with the lower limit at Vs1, as determined in § 3.82 with maximum weight, landing gear and wing flaps retracted, and the upper limit at the maximum structural cruising speed established in § 3.740. (4) The flap operating range—a white arc with the lower limit at Vso as determined in § 3.82 at the maximum weight, and the upper limit at the flaps-extended speed in § 3.742.

So now I especially like that she got to use the other one for fifty years. 

I knew it had to have Vne marked which could be done on the glass, as long as there's an alignment mark on the glass and bezel.   The rest is probably dependent on the certification details for each aircraft.

That's all magic IA stuff, right? 

[N201MKTurbo]

4 minutes ago, EricJ said:

So now I especially like that she got to use the other one for fifty years. 

I knew it had to have Vne marked which could be done on the glass, as long as there's an alignment mark on the glass and bezel.   The rest is probably dependent on the certification details for each aircraft.

That's all magic IA stuff, right? 

Yes, The IA test is all about looking up this stuff. There is practically nothing about fixing airplanes!

[tmo]

On 6/12/2020 at 8:47 PM, N201MKTurbo said:

There is practically nothing about fixing airplanes!

That was done during A&P, right? Just so I don't get confused on the distinctions...

[N201MKTurbo]

3 hours ago, tmo said:

That was done during A&P, right? Just so I don't get confused on the distinctions...

I was talking about the test for the Inspection Authorization.

[1964-M20E]

Well my 64E had the 50' markings and was certified IFR,  my 67F has the 20' markings IFR cert tomorrow if weather cooperates.

 

No wonder I find it harder to tell what altitude I'm at with my 67F.