IME (a £20k prop strike in 2002, brand new plane) and having seen loads of other likely scenarios, the most dangerous one for a prop strike is a grass to concrete transition. Often, the soil doesn’t come up to the concrete in a level manner so the nose wheel dips briefly…
I’d agree that grass is normally OK from the POV of dings in the prop – because most small stones are likely to be “submerged” in the soil, during the normal process of grass dying and new grass growing on top. The problem with grass is of course potholes (rabbits, etc).
Peter wrote:
IME (a £20k prop strike in 2002, brand new plane) and having seen loads of other likely scenarios, the most dangerous one for a prop strike is a grass to concrete transition. Often, the soil doesn’t come up to the concrete in a level manner so the nose wheel dips briefly…
I was taught to always cross at an angle for this reason.
Peter wrote:
I would guess there is a range of stone weights within which they get sucked up and cause damage. Smaller stones will get sucked up but won’t ding the prop.
Yes, as I said before, it seems that contrary to ‘popular belief’ operating high static rpm on bitumen leads to worse ‘dings’ than operating on gravel strips. Gravel is well weathered and round, whereas the stones that come loose out of bitumen are nasty sharp things.
Pilot_DAR wrote:
Run ups on the go might be a solution, though I hardly see the authority approving that
As part of routine maintenance an aircraft engine needs to be run at full throttle to ascertain that maximum static RPM is within limits. Equally, if I’m doing a short field departure I will ensure max static RPM.
At all other times I’m acutely aware of FOD when at any sort of power setting above idle whilst on the ground. Probably something to do with an (un)fixed drain cover 
which decided to rattle the propellor on a rather expensive TIO-540, resulting in a new prop and engine shock loading test.
Archie wrote:
Does the POH say that runups need to be done stationary? No? They would if there is a pressing reason. So, the approved document does not mandate stationary runups.
A random check of five Cessna POH’s in my library (172 to Caravan) just now confirms that each one states as a first step for the run up “Parking Brake – Set”. I suggest the intent is that the aircraft be stationary for a run up.
Re run-ups while taxiing – be mindful of brake overheating. And resulting brake fading and possible wheel pants fires, for example on a Cirrus.
When faced with bad taxiways or otherwise problematic conditions, there is always the option to do the run-up on the runway, traffic permitting.
Pilot_DAR wrote:
I suggest the intent is that the aircraft be stationary for a run up.
Point taken! So we’re back to looking for a run-up bay that is properly maintained/swept, or a grass area. Or as someone else mentioned, do a run-up on the runway.
What we haven’t talked about is the ability to do a ‘quick’ runup. I.e. if you are familiar with the aircraft, and proficient, a run up doesn’t need to take longer than a few seconds to check what you are looking for! Minimise exposure to stone damage.
Archie wrote:
a run up doesn’t need to take longer than a few seconds
On planes with full engine instruments (i.e. 6 EGT probes), I am looking for an EGT rise from each cylinder when switching to each mag. For this, I bring up the RPM to whatever is written in the POH for the run-up, normalize the EGTs on the engine monitor and wait they’re fairly stable (maybe normalize again), switch to one mag, look for 6 EGTs rising, switch back to both, look for EGTs falling, and switch to the other mag and look for 6 EGTs rising again. This is definitely longer than a few seconds. But I would be interested to hear if there is a quicker way to do this check.
To continue the discussion, how many cycles of the prop are really necessary? Notwithstanding that most POH say three times…
Twice. Once to check feathering and once to check general operation of the CS system.
