Standby altimeter diverts significantly

[daemotron]

My primary and standby altimeter are diverting . I was doing a series of flights without reloading the aircraft, and I don't know if it happened already on the first fligh, or just on subsequent flights after a couple of baro adustments for departure and arrival (always done for all three altimeters).

It's pretty much aligned on ground even on the last flown leg (given I use correct pressure setting for both, of course):

 

But with increasing altitude, diversion between both instruments becomes more outspoken (same pressure setting, of course):

 

At cruise I experienced more than 300ft divergence, which is pretty much for that... I was first asking myself if this could be one of the features (to have instruments not always perfectly aligned, just as in real life),  but given the magnitude of the diversion I think it's rather inadvertent (in an airspace with 1,000ft layers a diversion by 300 ft would be quite dangerous - having it in two aircrafts would bring them as close as 400 ft vertical...).

 

Edited April 9 by daemotron

[ixam500]

Quote

My primary and standby altimeter are diverting . I was doing a series of flights without reloading the aircraft, and I don't know if it happened already on the first fligh, or just on subsequent flights after a couple of baro adustments for departure and arrival (always done for all three altimeters).

It has to be so, I think Jan explained that in another post already. So basically the Primary Altimeter gets some fancy computer calculations to correct the altitude, while the standby one doesn't (its just static) -> they can divert up to 400ft.

Cheers,

 

Edited May 4, 2016 by ixam500
added quote

[JRBarrett]

My primary and standby altimeter are diverting . I was doing a series of flights without reloading the aircraft, and I don't know if it happened already on the first fligh, or just on subsequent flights after a couple of baro adustments for departure and arrival (always done for all three altimeters).

It has to be so, I think Jan explained that in another post already. So basically the Primary Altimeter gets some fancy computer calculations to correct the altitude, while the standby one doesn't (its just static) -> they can divert up to 400ft.

Cheers,

 

That is exactly correct. The primary flight displays receive their altitude from air data computers, which correct the altitude for temperature and airspeed. For flights within RVSM airspace, the altitude readout must be accurate to within +/- 45 feet maximum.

The standby altimeter is just a plain barometric altimeter - no computer involved, and barometric altimeters tend to become increasingly inaccurate at higher altitudes. The disparity between PFD altitude and standby is perfectly realistic.