A red aircraft icon means that AvPlan is receiving low quality location (position) information from “Location Services”, which is part of your device’s operation system, iOS. If you check the GPS error in the HUD, anything much more than a 5m error indicates poor signal reception.
Position error can be caused by a few different things:
You are indoors, so that the device's internal GPS cannot get a quality fix due to poor satellite signal strength. Try going outside.
Your iPad is low in your cockpit, and is shielded by the airfare from line-of sight satellite signals. Try placing the iPad closer to a window.
The GPS engine in your device is failing our has failed.
This last one is quite rare, but it can happen. The consequence will be large position errors (~50m), and more than likely there will be an error message in iOS Settings/mobile data. This is because the GPS resides alongside the SIM card circuitry in your iPAD, and they either both work, or they both have a problem. Whether or not you have a SIM card installed makes no difference if there is a problem with the circuitry. If this is in fact the case, you need to contact Apple to organise a repair or replacement.
Lastly, if you have not used your iPad for a long time (weeks or months) and it does not have a SIM card installed in the SIM slot, then the device may take a while to work out where it is. This is because the GPS almanac will have become out of date, and the GPS engine will have to download a new one from the satellite constellation in order to figure out which satellites to tune into and use. This can take as long as 20 minutes. If you use your device regularly the almanac will be maintained in a current state, and you will rarely notice a time lag when trying to use an app that uses location services shortly after device start-up.