Determining reliable altitude
 

Hi,

What is the best way to determine a reliable altitude given altimeters including standby altimeters are inop after takeoff? Also taking into consideration that radar altitude is inaccurate too. Will 1-in-60 rule be helpful in this case?

Thanks for the knowledge.

Regards

Your GPS may be indicating your height ? Your transponder might also still be sensing and emitting altitude, so ask ATC what they're seeing ?

In such a situation, also be sure to check the other air data instruments for validity. With a failure in the static pressure system, the air speed indicators are gone as well, so a good start would be the Unreliable Airspeed Indication checklist applicable to Your type.

Depending on the FMS installation and the nature of the failure, You might find air data readouts and/or GPS altitudes on some pages.

Surely if the altimeters are unreliable due to a feed problem the data going to the transponder will also be unreliable. GPS (if installed) is the way to go. And it will be altitude not height.

I’m not sure on the major jetliners, GPS altitude will be available?

What about on minor ones?

Use the weather radar ground return tilt angle until you get on the ILS glideslope at 6000ft/20nm.

What failure will cause loss of all barometric altimeters and also cause radio altitude to be inaccurate? Did the person who taped all the static ports also put high speed tape on the radio altimeter antennas?

This would probably be one of the worst things you can do. Your transponder does not have an independent altitude sensor and will be using the same suspect numbers as the rest of the aircraft.
This is what doomed the Aeroperu 757 - they were trying to fly using the transponder altitude (as relayed by ATC) and hit the ocean when they thought they were (IIRC) 6,000ft.
Radio altitude would be your best bet unless GPS altitude is available.

Are you able to elaborate please Capn Bloggs

The GPS will probably know it's height, but will have no way of displaying this to the crew as we don't use GPS heights. If you have no altimeter info then you've also got much bigger problems. You'll also likely have unreliable airspeed as well.

I assume its a pressurised aircraft, if so depressurise and see what the Cabin Altitude indicator says. Failing that has your phone/ipad got GPS?

Terrain function -> calibrated gain -> tilt-8.25 degrees(for a 3.5 beam like A320 WX radar antenna). The distance at which you notice the first returns, is your height above the ground in 1000 ft.

If WX radar inop, you can depressurize your cabin (provided you stay below 10000ft) and read the cabin altitude(adjust the value for non standard QNH).

It is available, and on the airbus I fly it can be seen both on the FMGC MCDU but also via the backup speed scale if equipped.

I would use delta P and a barometer that I have on me.
I have two barometers with me at all times, my watch, my phone, I'm pretty sure my ipad has a pressure sensor too.

This requires a bit of knowledge about standard atmosphere, but hey we're professionals.
FL30, 60, 100, 140, 180, 240, 300, 390 (Easy to memorize, +3, +3 then +4 +4 +4, +6 +6 and +9)

PMJI...
3 degree pencil beam weather radar, tilt down -8.5 degrees. Ground return distance is your absolute height. 10,000' paints ground at 10NM. 5000' paints ground at 5NM', enough to find an ILS GP.

Or, find the landing area radar reflectors and cook up your own final like back in the day.

Rule of 60, 1000'/NM is a 10 degree angle. Assumes an IRU stabilized radar airliner/big biz jet platform, otherwise compensate for deck angle.

It's just a radar tilt confidence check, in reverse. Mind the goats climbing hills and obstacles.

PMJI...
3 degree pencil beam weather radar, tilt down -8.5 degrees. Ground return distance is your absolute height. 10,000' paints ground at 10NM. 5000' paints ground at 5NM', enough to find an ILS GP.

Or, find the landing area radar reflectors and cook up your own final like back in the day.

Rule of 60, 1000'/NM is a 10 degree angle. Assumes an IRU stabilized radar airliner/big biz jet platform, otherwise compensate for deck angle.

It's just a radar tilt confidence check, in reverse. Mind the goats climbing hills and obstacles.

PMJI...
3 degree pencil beam weather radar, tilt down -8.5 degrees. Ground return distance is your absolute height. 10,000' paints ground at 10NM. 5000' paints ground at 5NM', enough to find an ILS GP.

Or, find the landing area radar reflectors and cook up your own final like back in the day.

Rule of 60, 1000'/NM is a 10 degree angle. Assumes an IRU stabilized radar airliner/big biz jet platform, otherwise compensate for deck angle.

It's just a radar tilt confidence check, in reverse. Mind the goats climbing hills and obstacles.