Adding a bit of an explanation from my stats, running down the whole thing. (Warning, numbers ahead)
I assume that every aerospace pilot gets 1 combat against another clan per year. The Scorpions win roughly the same amount they lose. So, looking at their ground forces (and using the baseline of FM: Warden Clans for their touman composition), they have a total of 628 aerospace fighters at full strength.
314 win their single trial against another clan per year, casualties in a win are, on average, 25%, so a total of 78.5 casualties. Of these losses, roughly 25% of the machines are beyond repair, leading to a total of 19.626 losses per year in won trials against other clans using the ground touman.
314 lose their single trial against another clan each year. Casualties ins loss are, on average, 75%, so a total of 235.5 casualties. Again, roughly 25% of the machines are beyond repair, leading to a total of 58.875 losses per year in lost trials against other clans using the ground touman.
I actually think the number of casualties on a win or loss are both closer to the 50% point - perhaps 40/60 or 33/67 - but the overall average ends up at the same point of 50%. There will be good years and bad years, but this is just looking at a hypothetical perfectly average year.
In space, they have a total of 200 aerospace fighters assigned to warships (these are the only concrete numbers we have, so if there any assigned to dropships or jumpships, then this number just increases). Again, each aerospace fighter gets in combat once each year with half of them winning and half losing.
100 win their trial against another clan, again there are 25% casualties, so a total of 25 casualties. Of these, roughly an eighth of them are beyond repair (or half as much as in ground conflicts). This means that roughly 3.125 casualties occur against other clans.
100 lose their trial against another clan, and with 75% casualties there are a total of 75 casualties. An eighth of these are beyond repair, leading to a total of 9.375 losses against other clans per year.
Lastly there are enough trials of position to fill out 20% of the entire touman (75% of these are expected to succeed). This means that there are 165.6 cadets trialing for full warrior status, so a total of 331.2 aerospace fighters are involved in these trials of position. There are going to be 50% casualties during these trials, but the more controlled environment means that only a twelfth of the casualties are beyond repair. This leads to a total of 13.8 destroyed machines.
Listing all the casualties:
Won ground trials: 19.626 fighters
Lost ground trials: 58.875 fighters
Won space trials: 3.125 fighters
Lost space trials: 9.375 fighters
ToP trials: 13.8 fighters
Total: 104.8 fighters (or 12.66%) losses each year.
Overall the losses are about twice as high as BattleMechs, even though I assume that 'Mechs are involved in twice as many trials each year. Most of this comes down to the more destructive environment - lawn darting, potentially being lost in space, and occasionally a more hostile repair environment than the typical 'Mech will see.
I encourage a picking apart of my numbers, as a lot of them are based on assumptions of survivability and the actual use of aerospace fighters in the clans.