“Just can’t wait to get on the road again…Goin’ places that I’ve never been…” – Willie Nelson.
At the beginning of each season, your ag aviation business undergoes a period of readjustment to get all the kinks out of the operation from receipt of order to finished job. It just takes a while after a break of any significant size to evolve from the initial awkwardness back to the smoothly oiled machine from the previous year.
However, as the season progresses, we may find ourselves “on the road again” in a completely new environment via an unfamiliar airstrip some distance from home plate. Whether we’ve seen the airstrip before or not, there is yet another period of adjustment where we must quickly become familiar with the specific requirements of the new location to ensure safe and effective aerial application operations.
There is much to consider: runway size, slope and surface, prevailing winds, obstacles, sensitive neighboring crops—the list is seemingly endless. However, the good news is that the new period of adjustment can be streamlined if we follow a few guidelines to keep us on track, a bit like taking a basic refresher course when the situation dictates. The only surprises you want are pleasant ones.
One learning experience with an unfamiliar airstrip I had early in my ag career involved a transit distance of a little over a hundred miles to treat a massive infestation of Bertha armyworms on canola fields. It was a last-minute arrangement with few details provided. Our ground coordinator said the farmer had told him he had an excellent airstrip he flew from regularly, so I went off my AT-502 with the mobile mixing rig enroute via road.
I guess everyone has their own version of what ‘excellent’ means. Upon arrival, I thought I had the wrong location dialed into the GPS as all I could find was an overgrown grass strip at most 1200 feet long and not more than 20 feet wide. If that wasn’t bad enough, it had a row of 40-foot grain bins at one end, a gravel road five feet higher than the strip at the other end, and it was oriented north/south, not east/west like the prevailing wind.
Luckily, the local municipality had a 3000-foot asphalt runway that was essentially unused. It served us very well during our weeklong stay. By the bye, the farmer did use his strip regularly, albeit with a Piper J-3 Cub on tundra tires. How long is long enough? If I had my druthers, I would always like to work from a 5000-foot concrete runway 150 feet wide oriented into the prevailing wind.
In practice, though, we must make accommodations to what is available. It’s difficult to give specific numbers for every situation because of the collective demands of aircraft type, load size, density altitude, and other factors. However, I recommend choosing a suitable runway length to assume you have an emergency situation requiring you to land with a 10-knot tailwind (because of high obstacles at the wind end) with a full load because the hydraulic spray pump had failed.
Given the rule of thumb that every 2 knots of tailwind increases landing roll by 10%, you’re looking at a 50% increase in rollout distance! Add to that a higher-than-normal approach speed at gross weight, and you have a real challenge.
How wide is wide enough? It should be sufficient to ensure no contact is made with nearby crops if your takeoff or landing is not what it should be and you diverge from the centreline. I’ve seen more than one aircraft twisted into scrap metal from a wingtip or spray boom getting snagged in a mature crop.
In short, never skimp on those things you can control. Have you ever heard the quip about the furniture store salesman who asked a customer what type of mattress he wanted? The customer asked if he had any small, used, cheap ones for sale. This is a bad approach for furniture, and it’s much worse for ag operations.
What about an unfamiliar airstrip with a noticeable gradient, i.e., one end is noticeably ‘higher’ than the other? Taxi to one end and read the altimeter, then do the same to the other end. Dividing the difference by the runway length will give you the gradient.
The rule of thumb is that each 1% of gradient changes the takeoff roll by 10% (uphill adds, downhill decreases). If the takeoff roll on a level airstrip is 2000 feet, a 2% gradient would increase that by 400 feet (20% of 2000) to 2400 feet uphill and decrease that to 1600 feet downhill.
Ideally, we would like to take off downhill to increase acceleration and land uphill to provide greater deceleration. However, we must factor into the effect of wind, where the rule of thumb is that each knot of headwind decreases ground roll by 1%, but every knot of tailwind increases ground roll by 5%.
The real kicker here is that if you find yourself, for whatever reason, having to take off with a 10-knot tailwind, your 2000-foot ground roll will increase by 1000 feet (50%) to 3000 feet! You can see that a tailwind is a really bad actor in takeoff performance.
Let’s not forget to increase your takeoff distance 10% for each additional 1,000 feet of density altitude. With a few calculations, you can get a head start on adapting to an unfamiliar airstrip.
I mentioned not skimping on those things you can control. The only exemption is load size. When flying off an unfamiliar airstrip, choose a light load for the first several trips until you gain experience with the airstrip’s load size. You can gradually increase the load once you have a good feel for the aircraft’s takeoff performance.
One final note. In this age of miniaturized gadgets, you can add several portable weather stations to your mobile equipment to provide critical information such as windspeed and direction at an unfamiliar location. This will make for peace of mind when you’re singing along with Willie about the pleasures of being back on the road again.
