Advanced Precautionary Search and Landings VAA

Back to basics

While we all (should have) learned to do a PSL during our early training, it often happens that the lessons learned are, at best, not practiced regularly or at worst, totally forgotten. Further, different instructors may teach different processes, and the training environment (as in the actual training area available to the airfield that you are flying from) may provide limited scope for different scenarios to be explored and different techniques to be practiced. You may well be taught how to perform a PSL in the training area near your home airfield. But once you have your Private Pilot Licence, Recreational Pilot Licence Navigation Endorsement or RAAus equivalent and start flying further afield, your home-grown skills may no longer be sufficient.

The options

You may be faced with a range of landing site options, from an established aerodrome with all the right facilities, through to an open field surrounded by hills, trees, power lines and other hazards.
In the best-case scenario, you may be looking at landing at an airfield for which you have all the necessary information (in Australia this can be found in the En-Route Supplement Australia or ERSA), but the field may be unfenced and prone to invasion by the local wildlife, for example. At the opposite end of the scale you may have little choice but a dirt road or fenced paddock. In the middle may be a suitable landing area but of unknown length and quality.

The Process

1. Make contact

Unless you know otherwise, always assume that there will be no radio signal available on the ground. The first thing to do while you still have the benefit of altitude is to make some radio calls and let others know what you are doing. In Australia the options in descending order of general usefulness are:

• Area frequency
• Nearest CTAF frequency
• MultiCom 126.7
• The pilot chat frequency 123.45.

In a more serious situation and when all other methods have failed, you may use the emergency frequency 121.5. This is almost constantly monitored by all heavy traffic.

Due to the line-of-sight limitations of your VHF radio, in the more remote areas, the chances of ATC (or indeed anyone below the flight levels) hearing your broadcast is slim. Of course, you remember the VHF rule of thumb for radio range to a ground station:

VHF Range in NM = 1.25 x √(Altitude in Feet)

For example, at 10,000 feet you could expect a radio range of 125NM. You can increase your odds by requesting “any heavy in the vicinity” to relay your message to ATC centre.

If your intended landing target is a rural station airstrip, if possible, try to contact the owner or manager of the landing strip by radio or phone. Maybe make a pass over the homestead. That will signal that you might need a ride, a meal and a bed. Just joking about the bed. Bring your own.

While you are at it, see if you can get some reports of ground level wind speed and direction from reliable sources such as local ATIS or AWIS stations, other pilots, etc.

2. Evaluate the chosen area

After checking the area for the best-looking landing site, it is time for the 5 ‘S’ questions.

• Size — does the area initially appear to be large enough to land your aircraft?
• Surroundings — are there large obstacles such as hills, trees or power lines around the target landing area, including what will soon become your circuit area?
• Slope — does the terrain appear to slope uphill in any particular direction?
• Shape – if the landing area is restricted by physical features such as fences or tree lines, where is the longest straight landing path?
• Surface — does the surface initially look flat and even enough, or at the very least, is it the best option available around the area?

3. Evaluate the wind

As a competent pilot, you will no doubt be constantly looking for clues about what the wind is doing during flight, even when there is no intention of landing either voluntarily or under protest.

Using technology

For the modern aviator with the benefit of GPS you should be constantly aware of your ground speed. By comparing that to your air speed, you should be aware at pretty much any time of the wind factor in the direction of your travel through the air. As an example, let’s say you are heading due east (090), your air speed is 100 knots and your ground speed is 80 knots. A simple mental calculation tells you that you are experiencing a 20-knot headwind. However, that does not mean that the wind is actually blowing from the east. Certainly, one component of the wind is from the east, but there is a 179/180 chance that there is another wind component of some sort blowing from either the north or south.

Of course, if you are well aware of the drift you are experiencing between heading and track, then you will have some idea of the strength of that second wind component. From those two pieces of data you can whip out your wind component grid graph and determine the exact wind direction and strength. That may take a while, but maybe your GPS can do all that for you. Even so, it will still only tell you about the wind at the level you were cruising. Unless your intended landing area is on cloud nine, or you continually monitor the wind changes as you descend (while you should be doing other things), that information may be of limited value.

The traditional way

The quickest and most reliable indicator of wind direction and strength is often provided by the smoke from fires on the ground, dust or other light material. This can also provide a good visual alert to phenomena such as temperature inversions or dust devils.

If there is a body of water nearby, the pattern of ripples on the surface may indicate wind direction. The calm water should be upwind, and the ripples downwind. Beware of using anchored boats as a guide to wind as they may have anchors fore and aft, or a running tide (or flowing river after rain) may have a partial or total influence. Also, terrain may influence wind direction in one area but not in an adjacent area.

Animal instincts

An old piece of folklore is that cattle in a paddock always stand with their backside into the wind. That may not be very reliable. Maybe they are just trying to make a point to another bovine that has failed to follow herd protocol. Silly old cow.

Another option is to watch the movement of cloud shadows over the ground. However, this only works on days with some (but not too much) cloud, in a decent wind and may or may not reflect surface wind direction.

Of course, if you are at an ALA there is always the windsock…maybe.

If you are still not sure about wind direction, and can’t call anyone on the ground, there is still another way to find out.

4. Investigate the target area

The first pass

First you need to descend to 500 feet AGL and make the first pass over the intended landing area. There is no need to take unnecessary risks by flying too low. This height is usually safely above all obstructions, although you should be aware of powerlines in valleys.

The purpose of the first pass is to measure the available landing area. This can be done using something like the following method.

Fly the length of the intended landing site at a constant speed and straight and level, in what you believe to be the upwind direction. In this case we will assume an indicated airspeed of 70 knots.

Using your trustiest timepiece, measure the time it takes to travel from one end of the useful runway to the other. Let’s say that takes 15 seconds.

The hard way

Now that we have speed and time, we can calculate distance using the familiar old formula speed = distance/time or, when rearranged, distance= speed/time.

Firstly, convert 70 knots (nautical miles per hour) to metres per second. You can use your iPad, whizz wheel or step through the following calculation if, like me, you can’t always remember formulae: From ERSA (or any one of several other sources that should be available in the cockpit), we can determine that 1 NM = 1.852 kilometres. Handy hint: This conversion rate is easy to store in the back of your brain if you remember that a nautical mile is very roughly around 2 kilometres, and the “.852” part of the constant is straight down the centre row of your calculator buttons. So, 70 knots equates to about 130 km/h.

Next convert kilometres to metres by multiplying the previous result (of 130) by 1,000 to give 130,000 metres per hour.

Finally, we can convert this back to metres per second by dividing by 3600 (60 x 60 = 3600 seconds in one hour), giving about 36 metres per second.

The easy way

Handy hint for dummies and pilots: If all this sounds too much like hard work, just divide 70 knots by 2 to get a close-enough answer of 35 m/s. This works because 1.852 x 1000 /3600 always equals 0.5 (and a bit).

Now that we know that we moved 36 metres each second, and did that for 15 seconds, it is easy to calculate distance as 36 x 15 = 540 metres.

If we use the dummies method, half of 70 knots x 15 seconds = 525 metres, which has a little extra margin for error for us real dummies. For an even easier example, if we travel at a constant 80 knots and it takes 12 seconds to traverse the landing area, the dummy’s available landing length is 40 x 12 = 480 metres. No calculator or lookup tables required.

Is the LDA sufficient?

Now that we know how much ‘runway’ we have available, we could use the landing chart or table in the POH to determine the landing distance required (LDR). However, the pilot’s skill level is probably the biggest factor that will vary the required distance. Work out your own numbers from experience. Preferably before the fact.

Landing roll factors

There are a number of factors that influence the length of the landing ground roll. Please consult the POH of the aircraft you fly for details.
It may be a good idea to find out the landing roll distance of your aircraft without using brakes until a slow taxi speed has been achieved. The use of brakes may not be advisable in cases such as standing water on the runway or long wet grass where the friction coefficient between the tyres and the runway surface is very low.

Pipers

In the case of a small Piper, you need to know the headwind component and the runway slope for one side of the table and pressure height and shade temp for the other. However, as we have calculated the distance available by flying with the existing wind, this effectively means that we can assume zero wind for the calculation input. If we also assume zero slope on the runway (we have no way to measure it from the air) we can draw a line across the runway distance required chart which will always be true for a level landing area.

Approaching from the other end of the landing chart, an assumption of 1,000 feet pressure height and 30⁰ shade temperature will be a reasonable average for many pilots, although it is easy to determine your own specific figures for where you regularly fly. In our above example the basic LDR is about 410 feet. At sea level on a standard day (15⁰ Celsius) the LDR would be 390 feet. This implies that the LDR will increase by roughly 1 foot for every 1 degree of increase in temperature.

Cessnas

For some Cessnas, a landing distance table is provided (see the example below). As you can see the inputs are similar (although in a totally different format), but weight is assumed at MTOW.
The bottom line is that you can pre-calculate the characteristics of your aircraft well before trouble strikes so that when it does, you will have all the relevant data easily available to make a quick and calculated decision.

Note: Better than calculating the landing distance, try the take-off distance. If you find that you need more distance for landing than take off, have a friendly instructor fix this issue.

The second pass (optional)

If you could not determine the wind direction previously from traditional methods or GPS, your final option is to fly the same length of the intended landing site in reverse. The direction with the longest time to traverse (given that a constant speed has been maintained) will be upwind, and therefore the correct direction to land into wind.

The third pass

Now that (one way or another) you know the wind direction, you can start to fly a proper circuit. This time you will fly the upwind leg at 250 to 300 feet AGL and have a closer look at the landing surface. If required, you can use 20 degrees of flap to allow slower airspeed while maintaining a safe stall margin. This time check for smaller obstacles such as animals, people, potholes, wires, etc. If you are satisfied the surface is suitable and there are no obstacles, clean up the aircraft and climb at the end of the landing area to 500 feet AGL for the final circuit.

If wildlife needs to be removed from the landing strip, make some noise by using full power. There is no need to fly too low. Make a pass and then re-join downwind, ready to land. If the wildlife looks like it might become a danger to your landing, go somewhere else if it is an option.

The landing

Fly a normal (albeit low-level) circuit. Perform the usual downwind checks then set up for a short field approach. A proper short field approach involves an approach on final that is at a much lower height than normal, with a very low airspeed and using the back of the power curve. If you are not comfortable flying on the other side of the power curve, just fly at a low speed approach (as given in the POH) for short field.

Some pilots don’t want to place too much trust in the engine when flying on the back of the power curve (reverse command). If you are not totally confident with this technique, ask your instructor for some help.

Go around

Never forget that you can always go-around. You shouldn’t hesitate to do this if the approach is not right or you see something on the runway at the last minute, even after you have touched down.

Alternates

If you can’t find an open field or suitable road, landing in a crop (like sugar cane) can be a good alternative and you won’t need as much landing distance. The field surfaces are usually fairly even so the machinery can harvest properly. The taller the crop the shorter the ground roll. However, if the landing doesn’t injure you the farmer might.

Aero Circus has recently published a book called Refine Your Flying Skills. This article is an extract from the book, which explores a range of techniques pilots can use to enhance their professionalism when behind the yoke. See the bottom of this page for more details or head over to aerocircus.com.au.