Thats really important because if the mars plane gets overturned or somehow in a non-upright state, righting it top side up, might be impossible, being as much as tens of millions of miles away.
It seems to me thinking about it that I have not seen a suitable completely flat area in all the Mars pics I have seen, (a lot) There must be some , like sand, but not a real lot, and mapping would have to be done to locate it.
Here on Earth, with people to fix things, one way around the dearth of airports wherever you wantthem is a parasail-or paraplane like setup? On Youtube there is video of some guy living in the midst of the US midwest (very flat for hundreds of miles) going to a McDonalds several towns away for a hamburger with his paraplane.
This is a FAR more important factor:
But takeoff and landing on a "runway" of sand and rocks might be harder. Perhaps a mars VTOL