Spotting

Disclaimer

This blog post is aimed at trainee skydiving pilots unfamiliar with the sport. While the notes are useful, they should complement hands-on training and real flights. Keep in mind that some details might not be clear when taken alone. Calculations suit my training techniques, but other airfields could differ. Always follow the procedures of your airfield, as rules vary by country. For instance, in some countries, pilots are held responsible for ensuring the jumper's flight path to the PLA, with potential consequences if a skydiver enters a cloud. Conversely, in the UK, jumpers are accountable for ensuring a clear and visible flight path back to the PLA. It's crucial to fully comprehend your obligations within the country's regulations where you're operating. Should any discrepancies arise between my notes and your location's regulations, always prioritise the accuracy of your local regulations.

Introduction

Parachute "spotting" is the term used when identifying and selecting the ideal exit location from an aircraft over a specific point on the ground to assist the parachutists arriving within the designated landing zone known as the Parachute Landing Area (PLA)

To understand the origins of certain things, it's necessary to look back to the past when round parachutes and sturdy legs were prevalent.

History of Spotting

In the early stages of parachuting, the absence of any steering left jumpers entirely at the mercy of the wind. Assessing and determining the exit point became a skill entrusted to a few highly skilled individuals known as the “Jumpmasters”. Spotting involves positioning the aircraft upwind of the designated landing area, PLA, exiting the aircraft from a specific spot over the ground, and then relying on the wind to carry them back to the intended landing area.

Unlike today, where there seems to be an app for every conceivable task, many drop zones in the sixties lacked easy access to up-to-date weather forecasts. Instead, they observed the sky and best guessed it. If the conditions looked promising, the aircraft would ascend to a height of 2,000ft, the planned opening altitude for the jumpers' parachutes back then.

The pilot would position the aircraft to fly directly over the centre of the PLA into the prevailing ground wind direction. At the same time, the Jumpmaster would stick their head out of the aircraft door to provide heading corrections in multiples of five degrees, either to the left or right or sometimes a combination of both. For instance, a call of "10-right" indicated that the pilot should make a shallow turn of 10 degrees to the right. Typically, a sturdy stab on the rudder pedals is usually sufficient.

Once positioned directly above the PLA, the jumpmaster would throw the Wind Drift Indicator (WDI), affectionately known as "widdy." This WDI is a 10-inch wide, 20-foot long strip of crepe paper, usually coloured yellow or red to be easily visible against the ground. Weighted at one end, it imitated a parachutist's descent rate and drift under a non-steerable round canopy.

After the WDI was released “widdy gone”, it's the pilot's job to manoeuvre the aircraft to fly around (climbing turn) the descending WDI allowing the jumpmaster to monitor where it eventually lands. Subsequently, a straightforward procedure was followed, wherein the pilot flew upwind for the same distance beyond the PLA as the WDI had originally landed downwind from the PLA. For student static line operations, some DZ's would run in at 1,000ft for the WDI and double the distance for the static line drop at 2,000ft.

The image below shows where the WDI landed, having been dropped over the centre of the PLA. Jumpers exiting upwind by the same distance will drift with the wind, landing inside the PLA - hopefully.

During the run-in (the phase of flight starting approximately 2 minutes before the planned exit), the pilot guides the aircraft along an imaginary line drawn from the WDI to the centre of the PLA and then continues towards the exit spot. However, without any fancy instrumentation back then to show drift and distance, it was challenging for the pilot to accurately determine their exact position above the ground. Therefore, the Jumpmaster again would have their head out of the door providing corrections.

In the United Kingdom, frequent cloud cover often obstructs the pilot's view of the route to the PLA. Consequently, there used to be much pointing and shouting from those in the back of the aircraft, which had a better view of the surroundings through the open door than the pilot. If fortunate, the aircraft might have been equipped with a functional VHF Omni-Directional Range (VOR) and possibly Distance Measuring Equipment (DME). If exceptionally fortunate, the pilot would know how to use them.

However, when initially approaching from a fixed radial using the VOR, or perhaps a trusty ground feature, the direction of the approach might not align with the wind direction that day. A "ninety right" turn request from the Jumpmaster and a pilot executing a standard rate one turn would seldom resolve this issue. It was not uncommon for the Jumpmaster to call for a "go-around," meaning the pilot should circle back and attempt the approach again to find a better alignment with the wind direction.

Upon reaching the desired exit location, the Jumpmaster would shout "CUT" to the pilot, signifying the necessity to decrease the RPM and minimise prop wash. An "EXIT" call would quickly follow this. The jumpers would then pile out the aircraft as quickly as possible.

The exit window around the ideal spot was relatively small. The jumpmaster would always call the cut & exit a bit before the spot to allow time for the jumpers to climb out. But, departing prematurely could lead to them being carried downwind of the PLA, while delaying the exit might cause them to land beyond the intended area. In situations where the aircraft veered off the wind line, the distance might have been acceptable, but the wind would blow them down the side of the PLA. Depending on the surroundings, this could significantly spoil the jumpers' day.

In those early days, jumpers began experimenting by cutting holes in the back of their parachutes. This clever modification allowed the air to escape from the rear of the canopy generating a modest 6 to 8 knots of forward speed. Pulling on the lines could manipulate the parachute's orientation, enabling them to run with the wind when exiting late or hold when exiting early and avoid obstacles on the ground. This improvement increased their chances of landing on the PLA, as they could now adjust their position in the sky to intercept the desired flight path to the PLA. In the event of a parachute malfunction, the typical round reserve was not steerable, so having a good exit spot would hopefully mean the jumper and their jettisoned main parachute would still land on the DZ.

Spotting Today

In the present day, we have fully embraced the benefits brought about by technological advancements. Due to easy internet access and GPS navigation, both skydivers and pilots can now instantly access up-to-date weather information. This capability allows for more precise planning of the exit spot. Convenient weather apps, Windy, Winds Aloft, and resources like the UK's Met Office 214s offer practical tools that minimise the necessity of depending solely on personal observations and speculation.

Additionally, progress in parachute technology has led to the development of Ram-air canopies. These canopies incorporate inflatable cells that shape into an aerofoil parachute, capable of achieving speeds exceeding 20 knots.

The video below shows just how fast parachutes can fly in the hands of some very experienced skydivers.

Drop zones today in the UK have embraced larger aircraft to accommodate groups of up to 18 or more skydivers. With skydivers now able to navigate back to the PLA under their ram-air canopies, the significance of spotting has diminished in one aspect. Still, it has become even more crucial in others.

A skydiver's ram-air canopy typically has an average glide ratio of around 2:1 in nil wind conditions. This means the skydiver can travel approximately two units forward for every descent unit, whether in meters or feet. For instance, if a skydiver is under their ram-air canopy at an altitude of 2,500 feet (762 meters), they can glide roughly 1 mile (1.6 kilometres) to land in the middle of the PLA. Similarly, at 5,000 feet (1,524 meters), they can glide approximately 2 miles (3.2 kilometres) to reach the PLA.

The subsequent examples of distances and speeds, including these, are conservative.

It is important to note that while the glide ratio of a ram air canopy allows for some horizontal movement, skydiving canopies are primarily designed for a controlled descent and landing rather than extended horizontal flight. It is not a common practice to fly the aeroplane in any old direction and have all the jumpers exit roughly within one mile of the PLA, as there are other considerations and procedures involved in skydiving operations.

The wind influences a skydiver's glide distance on a ram-air canopy. Like powered flight, encountering headwinds leads to decreased ground speed. Conversely, tailwinds have the opposite effect, propelling us forward. Likewise, a skydiver's canopy functions as a glider, exchanging altitude for velocity to generate forward movement, but their decent rate will almost remain constant during the flight. When faced with reduced ground speed due to a headwind, the canopy’s glide ratio decreases accordingly. Flying into the wind may see the jumper coming straight down while flying with the wind will see them cover a fair distance across the ground.

Skydivers have a greater ability to deal with being off the wind line by altering the heading to give them a track back to the PLA. Skydivers refer to this as crabbing across the wind rather than heading and track, but it’s the same principle when dealing with the crosswind.

The requirement to throw a widdy has changed in the UK, so it has mostly been removed from the day-to-day jumping program. The widdy is still required for Water jumps, demonstration jumps, or when the first lift contains students (Not Tandem students) Further information on when a widdy should be used is found in the British Skydiving Manual. Section 3 and Section 8 as of August 2023– search the manual for WDI for any further updates/changes. https://britishskydiving.org/wp-content/uploads/2022/06/Operations-Manual-Jun-2022.pdf

Not all skydivers open their canopies at the same height above the ground. In the UK (2023) the following minimum canopy opening heights should be observed.

British Skydiving B License skydivers and below 3,000ft AGL

British Skydiving C License skydivers and above 2,500ft AGL

British Skydiving Student Tandem Skydivers 5,000ft AGL

British Skydiving C License skydivers, on display 1,500ft AGL

(These heights are when the canopy should be fully inflated and under control.)

Skydivers may wish to open their canopies higher the minimum listed above, sometimes a lot higher. But this should be discussed with the Chief Instructor, Ground Control and Jump Pilot. Unplanned high openings (premature opening) should always be taken into consideration these malfunctions could be when the main canopy or reserve canopy is deployed due to handles snagged or worn closing loops snapping during freefall. 

From the 214 data example above, our initial focus lies on wind direction within the 1,000 to 5,000 feet range, encompassing the parachute deployment heights. In this example, we observe variable directions between 020 and 040 degrees when assessing wind direction. Taking the mean, we opt for a run-in direction of 030 degrees.

In terms of wind speed, averaging between 1,000 and 2,000 feet yields 15 knots in this instance. Considering the typical parachute speed of 20 knots, we deduce that most parachutes will experience a 5-knot ground speed flying into the wind and a 35-knot ground speed flying with a tailwind. The descent rate remains constant, roughly 1 minute per 1,000 feet (300 meters).

Expanding on the earlier example and referencing the chart, we note that a parachute flying 2,000 feet into a headwind could cover 0.16 nautical miles. Calculating a 20-knot forward speed against a 15-knot headwind yields a 5-knot ground speed. A two-minute flight from 2,000 feet (600 meters) corresponds to 0.16 nautical miles on the chart - (2min on the bottom horizontal scale and 5kts on the side vertical scale). This allows for the Exit spot to be 0.1 nautical miles before the PLA, indicated as -0.1nm (rounded down from the 0.16).

Those exiting later will be running with the wind back to the PLA. A parachute at 2,000 feet with a 15-knot tailwind can cover 1.16 nautical miles. The 20-knot forward speed combined with the tailwind's assistance results in a 35-knot ground speed. After a two-minute flight from 2,000 feet (600 meters), the chart shows a distance of 1.16 nautical miles. Thus, the latest exit point could be extended to 1.1 nautical miles, represented as +1.1nm (rounded down from 1.16).

The spot calculations are now happening at the aircraft's pilot's end of the aircraft and not the jumpmaster's end, by the jump door. It’s now the responsibility of the jump pilot to call the exit. The pilot will call for the door to open before the exit spot, either verbally or by switching on the red light visible to the jumpers. When the spot is reached either again verbally or by switching off the red light and then switching on the green light to signal the aircraft is ready for the jumpers to exit. – it is still the jumpmaster’s responsibility to check that the spot is correct and that the PLA is visible (UK rules). If, for any reason, the aircraft requires a go-around or the jumpers should stop exiting, the pilot puts on the red light and turns off the green. Some aircraft operations use an amber light as well as red & green, the exact use is outside of this briefing as the UK typically only uses verbal or red & green signal lighting.

Exit separation

As we have seen, the actual spot above the ground has a bigger window, with the skydivers using ram air canopies rather than round parachutes. But we now have the problem that skydivers need plenty of space around them when they deploy these canopies. These types of canopies don’t always open on a heading we expect, and two canopies opening close to each may turn towards each other, risking an entanglement. Two canopies flying towards each other will see them have a combined closing speed of over 40kts. This means that instead of everyone exiting simultaneously, we need to give a few seconds of exit separation to enable sufficient space between them during deployment.

The time between jumpers or groups of jumpers depends on how fast the aircraft moves across the ground. To help better understand this, imagine the aircraft hovering above the ground. As each person exits, they will fall and open at the same point, so we would need at least 30 seconds between exits to ensure the previous jumper has moved out of the way. Now if this aircraft is moving at 120kts across the ground, then 30 seconds would see 1 mile between each skydiver, which is too much as the last jumpers to exit would end up too far away to make it back to the PLA. 

The optimum distance between skydivers/groups is around 1,150ft (350m), which gives about 17 seconds for those on canopies with a forward speed of around 20kts to react to a head-to-head situation. This distance will give those on faster canopies, 25kts, around 15 seconds to react. As with all flying, the pilots/skydivers must alter their course to the right when approaching each head-on or nearly so.

Once again, calculating the exit separation has changed over the years. A few decades ago, jumpers would wait until they observed the skydiver or groups of skydivers were about at the 45-degree angle behind the aircraft before exiting themselves.

As time passed, we started looking at the wind on the nose of the aircraft to give us separation. This was a simple calculation of Indicated Airspeed minus ground speed displayed on the GPS.

IE 80kts indicated, minus 60kts ground speed equals “20kts on the nose”

After receiving wind speed information, skydivers employed diverse methods to compute the necessary separation. Many relied on the memory of the repetition, and some had an equation involving wind speed divided by 60 and multiplied by 15. It's important to note that outcomes differ when using GPS-based ground speed in conjunction with indicated airspeed, as you should be using true airspeed with true ground speed.

Lately, just the ground speed is used for separation calculation, which can be applied to the chart below.

Start with the ground speed (vertical scale), move along to the green area, and then up to the seconds (top horizontal scale).

Remember, triangulation used by the GPS gives a true ground speed based on fixed-orbit satellites. On a day with nil wind at altitude, a ground speed of 95kts will have jumpers believing there is a tailwind of 15kts based on our indicted airspeed of 80kts. This raises the excitement level somewhat, with everyone shouting to hurry up. Of course, this is incorrect thinking as true airspeed may be around 95kts while indicating 80kts.

True airspeed is worked out by TAS = EAS x sqrt (p0/p), easy!The rule of thumb method is to add 2% for every 1000ft (300m) of height IE 2% of 80kts = 1.6kts per 1,000ft (300m). At 10,000ft, 10 x 1.6 =16kts, 16kts plus IAS of 80kts gives us a rule of thumb TAS 96kts. A ground speed of 95kts means it’s practically nil winds at 10,000ft.

Some GPS/EFIS show true airspeed, and some IAS gauges have bezels around the outside (Cessna caravan), allowing you to set the height against temperature or a fixed inner scale based on the 2% rule. In reality, the difference equates to very little change on the chart. But if you are flying along faced with nil wind up top while trying to remember all this, just shout “7 to 8 seconds” when asked.

Some drop zones have the pilot reporting the separation time from the chart direct to the jumpmaster removing any confusion over the IAS virus TAS.

All Skydivers in the UK are restricted from jumping in winds that are over 20 knots measured on the ground. For students (not Tandem students), the limit is 15 knots. There has to be some discretion applied to those limits, as the 214 example below shows the wind on the ground is within limits for all, but at 2,000ft (600m), most will be flying backwards at 5kts until 1,000ft (300m) and even faster backwards above this height. On days like this, it is not uncommon to see a jump limit applied. This may be a C license above only, 200 jumps and above, or a combination of both. Other factors may be applied on an individual basis. Setting these limits is the responsibility of the Chief Instructor, but you may be asked for input about the conditions.

Elevated upper winds can induce drift among skydivers on the freefalling part of their descent “freefall drift”. This drift might result in the initial group being carried back to a position that, following parachute deployment, falls short of the intended spot, thus causing them to land short of the PLA. Due to the distinct orientations during freefall (belly to earth, head down, head up), accurately estimating freefall drift can prove challenging.

When upper winds are particularly strong (exceeding 30 knots) from exit altitude down to 5,000 feet or 2,500 feet, it's advisable to incorporate an additional 0.2 into your calculations. For instance, if you initially determine a jump run starts at +0.4, adjust it to +0.6.

In cases where winds are high at the exit but quickly diminish to 20 knots or less during the descent, the impact of freefall drift can be largely disregarded. - (this is a rough rule of thumb approach)

Exit Order

We now understand the spot and the exit window (jump run). We understand the separation requirement and how this alters to fit the skydivers with the jump run start and finish. The third variable we have is the exit order of the skydivers and their planned discipline.

Typically, the skydivers that plan to open their canopy at the lower limit shown in the list above will exit first. And the skydiver planning to open at the higher limit goes last—experienced C license, followed by solo students and then tandem Students. Some of jumpers will look to leave as one group, normally referred to as an x-way, where the x is the number of people in that group IE a “6-way going first” means six people in a group leaving at the start of the jump run.

For us, we are interested in how many groups are going to be exiting. A group can be one person or six or more. Once we know how many groups and the required separation, we can start thinking about how long our jump run will be and whether the number of groups will fit within the jump run. Using the first example with the steady 15kts of wind, we know the start of the jump run is -0.16, and the end is +1.16. Effectively, we have one mile from start to finish. If we have five groups and the agreed separation between the groups is seven seconds. We need 28 seconds (the count starts after the first group leaves). If our ground speed is about 65kts, then we are roughly travelling a mile a minute (1.083 miles per minute for those that want the maths). We only need roughly 30 seconds for the groups, and we have 60 seconds of jump run. If more groups, for example, 12 groups, were planning to have open parachutes by 2,500ft, we would consider two passes and warn the last groups you will call “go around” at the +1.1nm marker. If some groups were planning to open by 3,000ft, then our jump run can extend, and if the last groups out are tandems, then we can extend even further as they will be open by 5,000ft. meaning we can complete the jump run with one pass.

Skydiving Disciplines

We touched lightly on free fall drift, but there are also disciplines within skydiving where the jumper deliberately moves across the sky. Tracking groups and wingsuit flyers effectively fly through the air and can cover distances measured in miles rather than fractions of a mile.

Tracking groups exit the aircraft within the jump run as planned, but they will look to turn off the aircraft heading and track away from the jump run line. It is their responsibility to ensure their chosen path does not interfere with other jumpers and that their route brings them back to an area where they can make it back to PLA after deploying their parachutes.

Wingsuit flyers can cover several miles, and although their deployment heights are within the lower scale, they will typically exit last as their freefall decent rate is much slower. It is not uncommon for a wing-suit group to wait for over a mile after the group in front left the aircraft before they exit. Once again, they are responsible for ensuring the flight paths keep them clear of other jumpers and brings them back to a position where they can land on PLA after deploying their parachutes.

When large groups of wingsuit flyers want to jump together, they will require a different spot and run in. Don’t Panic! It uses all the principles we have covered so far.

Wingsuit flyers will typically take longer to exit than those without wingsuits, and intercepting each other in the sky is challenging. To assist, the jump run is flown perpendicular to the normal jump run line, anywhere from 2 to 3 miles upwind. The jumpers will wait until there is roughly a 20 to 30-degree angle beyond the wind line before exiting. This is roughly around the 0.3nm mark from the run-in line. As each jumper exits, they will look to cut the corner and formate with the first jumper to exit. Once again, they are responsible for where they open.

Canopy Formations encompass a technique where skydivers release their parachutes shortly after exiting the aircraft. These formations are usually constructed along the jump run line, aligned with the wind direction. Because of the extended flight time under the canopy in shifting winds and varying speeds at different heights, the designated exit point might substantially differ from that used by fellow skydivers on the same day. While you might be requested to provide input, the skydivers generally collaborate to determine the appropriate exit location for this type of jumping.

Summing Up

That’s all you need to know, or perhaps even more than you need to know. Certainly, many things you didn’t know or even knew you needed to know. Who knows!

Remember that the spot can be modified after the first lift, so we aim to get it roughly correct.

If you hear absolutely nothing about the spot after the first lift, well done, you have done a great job!

Terminology

Running IN – height and direction established approximately two minutes before exit.

Jump Run – the time between the first and last jumper exiting the aircraft

Cut – A request from the jumpmaster to reduce the power/prop wash so they can exit

WDI (widdy) – Wind Drift Indicator thrown form 2,000ft

Red Light – door open (or call door open)

Green Light – Exit signal (or call Exit)

Free Fall Drift – Jumpers blown across the ground while in free fall

X Right or Left – A request to change the heading by x degrees to the right or left

PLA – Parachute Landing Area

DZ – Drop Zone, the area which covers some if not all of the airfield.

Spotting – The art of determining the exit spot above the ground.

Exit Separation – The time between groups exiting the aircraft.

Using the Garmin GPS unit with the information from above is here