What is the highest a reg. number can be read?

[Contacttower]

I while ago I looked up and saw quite a low flying PA28, so low in fact that I could clearly read the registration printed on the underside of the wing.

Does anyone know what is the highest a registration can be read from the ground with the naked eye (assuming good eyesight)?

[slim_slag]

That's nothing. I've been able to read the registration on A340s on downwind into a local airfield when they are doing touch and gos. Amazingly quiet for the size.

You should be able to work it out if you take normal vision to be 6/6 and estimate the height of the letters on the wing. Calculate the angles, simple maths/physics. The A340 wing subtended an angle that was approx the angle subtended by the moon (give take 50%), so I guess I could work it out if I wanted.

[Mark 1]

If you use the Snellen chart as a comparison, standard, or 6/6, vision is defined as being able to read a character that subtends an angle of 5' of arc.

The underwing registration is at least 500mm high. So this would subtend 5' at about 300m (1000') distance.

I believe it is the intention that they could be easily read if the aircraft is closer than 500'.

[Contacttower]

That's quite helpful thanks, the plane in question wasn't particularly low, but it was over a built up area and that was what made me wonder about reading the registration.

[gcolyer]

What is the highest a reg. number can be read?

Highest what?:}

[Contacttower]

I thought it was implied in my question that I meant AGL, hence the reference to low flying.

[davidatter708]

I have mild long sightedness but very mild I can read reg's in the circuit at 1000 and joining at 2000 but it depends on the backroud colour of the aircraft and the reg colour. So much for the rule if someone can read your reg your too low :p
Dave

[False Capture]

So much for the rule if someone can read your reg your too lowNot if you're flying upside-down.:cool:

[SkyHawk-N]

Or if you fly an N-reg :ok:

[Whirlygig]

So much for the rule if someone can read your reg your too low

No, if you're too low, it means that your registration number can be read but it does not mean, ipso facto, that if your reg can be read, you are too low!!

Best to wait until you can see the whites of their eyes :}

Cheers

Whirls

[TheGorrilla]

Better idea.... Don't have a reg!