Another guest blog from retired pilot Rudy Jakma. This on the topic of banner towing – where light-aircraft trail a banner behind them, to be read by people on the ground. Rudy has extensive experience of banner-towing, particularly from the earlier parts of his career, with around 4000 hours logged, and around 1000 banner pick-ups. His experience even pre-dates his flying career, as he worked as a 16-year old at a local aerodrome, helping to prepare banners to be picked up.
Last week, during the election campaign in the UK, a light aircraft crashed injuring the pilot and his passenger. It had been involved in a banner-towing flight on behalf of a political party, and the passenger, Nigel Farage, was an official of that party and standing as a candidate.
On Sky News, an “expert” proclaimed that towing a banner would have put the aircraft under abnormally high stress, increased by the weight of the passenger and that this would have meant that the flight (which sounded as if he meant the entire flight) was more hazardous due to the presence of the banner. Where do they get these experts from?
From the TV footage of the wreckage I identify the aircraft as a Polish-built Wilga. This is a purpose-built utility aircraft. Towing objects, be they banners or gliders, is well within its structural capability.
All aircraft used for towing must be approved according to manufacturers’s recommendation and are fitted with quick-release tow hooks. The aviation authorities will follow manufacturers’ guidelines and may impose further limitations before they approve a certain aircraft type for towing operations. This ensures that towing an object will never allow stresses to be imposed on the structure that could compromise the structure in any way, be it due to deformation, stress or metal fatigue. The limitations will be published in the aircraft operating manuals and, if deemed necessary, also posted on placards in the cockpit.
The engine will not be subjected to any excessive demand for power, During cruise flight when towing, the engine usually is running at lower RPM than required for normal cruise flight. But, as banner towing always involves a speed well below normal cruise fllght, it may well impose a higher than normal nose attitude. This in turn could in some aircraft cause the engine to run hotter than normal. In such cases, manufacturers of airframe and engines may specify installation of an extra oil cooler and / or modifications to the engine cowling if the aircraft is used for (prolonged) towing operations. Some aircraft are recommended to fly towing operations with one stage of flap setting extended which will stabilize the aircraft and lower the nose attitude – and stall speed.
Other than these considerations, there are no unusual precautions for towing operations. The weight of the banner is never a factor. It weighs less than a passenger. In the air, it causes drag. Lots of it. A typical full-size banner may cause more drag than a typical glider. As drag increases exponentially with increasing airspeed, this is the main reason why a banner is always towed at low speed. It also allows more time for the public to read the message. Typically, depending on the type of aircraft, it will cruise at speeds between 45 and 75 mph.
The presence of a passenger would have meant that there would have been restrictions on the size of the banner. From the TV footage I gather that the size of the banner would not have been the cause of the crash, nor would it have been a contributing factor. In many countries, carrying a passenger during towing operations is prohibited except if necessary for the purpose of checking out another pilot. The size of the banner would have been reduced in compensation.
The Wilga is a STOL aircraft: Short Take-Off and Landing. This means it can fly at very low airspeeds under full control without stalling. Cruise speed whilst towing would therefore be around 60 mph. Possibly even lower if necessary.
The aircraft can not take off with a banner attached. It will drag along the surface and will, if not preventing it from getting airborne certainly have the effect of an unacceptable prolongation of the take-off run. It also will more than likely cause damage due to tearing or friction to the banner. The aircraft does not land with the banner attached, either. Not normally. Before landing, the aircraft will make a low pass over a designated area on the airport and release the banner before it joins the traffic pattern for landing.
The banner is borne aloft by means of a pick-up manoeuvre. A grapnel on a line, usually about 30 – 40 feet in length, is attached to the quick-release hook at the tail of the aircraft. Attaching the cable requires opening and closing of the tail-hook on the aircraft, and this in itself is a check to ensure smooth operation. The banner itself is laid out in a pre-determined area on the airfield. A towing line is attached, ending in a loop. The loop is strung over two forked poles. A batsman or operator of a portable 2 way radio guides the pilot who will catch the loop with the grapnel during a low pass, followed by a fairly steep climb to allow the banner to peel off the surface, and minimise any dragging of the banner along the ground.
The banner pick-up procedure is the only time when the aircraft is routinely exposed to a higher than normal risk. If the climb is too steep (mainly a novice’s mistake) the aircraft may stall. Even if this happens, chances of survival are high as the banner will stabilize the aircraft which will often result in no more than a very hard landing. Another mistake, potentially lethal, is when the pilot thinks they have missed and puts the aircraft in a steep turning climb to quickly come around for another try. This can result in a spin from which, so close to the ground, recovery is not possible.
I have learned always to climb straight ahead to a safe altitude first which probably saved my life on one occasion when during an unassisted pick-up (without ground crew) I did not see the loop during my run-in. I came a bit lower to see what happened and noticed that the loop had fallen off the forked poles and was lying on the grass surface of the pick-up area. This meant I would have to release the grapnel, land, set up the loop over the forks and take off again. As I did not want to spend a lot of time searching for the grapnel I intended to come around again to drop it beside the banner. Even so, I climbed straight ahead and was just considering to start my turn when I felt a jolt. The grapnel had engaged and had picked up the banner from the grass – 1000 to 1 chance! The banner was hanging perfectly.
During all my years in aviation, I have only seen one pilot killed as a result of banner towing. It was a total freak accident. The aircraft was a Tiger Moth, now a priceless classic biplane, but then an ageing trainer and workhorse nearing the end of its useful life. Forward visibility from the rear cockpit – the normal position of the pilot during solo flight – was limited. The pilot had come in too low and had picked up the banner with the undercarriage. It could not be released so he had to land with it. The drag of the banner on the main wheels pulled the aircraft upside down. The pilot was not injured at all. Tragically, he panicked and released his safety harness before assistance arrived on the scene. He fell on his head and broke his neck.
According to the news, the recent crash took place when the pilot was coming in to land, at the end of the flight. I dispute the “expert’s” statement that towing a banner is putting the aircraft under any kind of risk or excessive strain except during the actual pick-up. And even then, the stresses imposed on the aircraft are well within safe structural limits, determined by the manufacturers and approved by the airworthiness authorities. According to the news reports, the aircraft had become safely airborne so the phase during which it had been exposed to a higher theoretical risk had been passed in safety. At the time of the accident, therefore, the aircraft should have been under relatively safe conditions of flight. A shot of the wreckage of the aircraft being pulled upright clearly showed petrol leaking from a ruptured tank. Therefore this indicates that the aircraft had not run out of fuel.
So what caused the crash? I have nothing to go on except projecting my (ample) experience with banner towing on the meagre news reports. So all I can come up with, awaiting results from the official investigation, is an educated guess.
In an aerial shot, it seemed that the banner was lying in the field directly behind the wreckage. This would seem to indicate that the banner may not have been released at the time of the accident. As I already mentioned, an aircraft when towing a banner will fly at very low but perfectly safe airspeed. The banner will be suspended behind it and trail approx. 15 feet below the aircraft’s flight path. It is not impossible that the pilot misjudged the altitude of the banner when coming in to drop it.
When there was a bit of a crosswind (according to the newsreader there was indeed a strong crosswind), we used to come in for the drop in a shallow dive. This would ensure that the banner would be at least at the same altitude or higher immediately prior to the drop. This in turn would allow us to come very close to the ground and at the same time preclude the banner drifting out of the allocated drop zone, perhaps too close to – or even over – the runway.
I suspect the pilot may either have been attempting to drop the banner, or may have intended to make a low pass with the banner for the benefit of the public and press, especially as he had been carrying a politician as his passenger.
Either way, my hypothetical explanation is that the aircraft came in too low and the banner, still attached, struck the ground. This would have caused a sudden and very abrupt deceleration resulting in a stall from low altitude. The aircraft would have struck the ground very hard. The tow line attached to the aircraft usually includes a weak link of calibrated maximum strength, designed to snap if the design load is exceeded. This may have detached the banner from the aircraft at the very last moment. Without the banner it might well have nosed-over.
Please be aware that this is no more than a guess!
Paul Jakma's Blog 
Graunch. said
There is some discussion on the Internet as to the existence, or not, of a Spiral flow of air or a cylinder of rotating air behind the propeller of a conventional tractor aircraft. If this rotating cylinder of air exists, how can a towed banner remain upright and not twist?
Rudy Jakma said
An excellent question.
The air behind the propeller indeed, inevitably, makes a “curve” as it spirals around the fuselage. All pilots flying single-engined aircraft know this. American-built aircraft engines in general turn clockwise (seen from the cockpit), British-built ones the other way around. During take-off this spiral effect is at it’s maximum as the forward speed of the aircraft (the airspeed) is low and the engine runs at full power. Therefore pilots know that they have to compensate by feeding in some rudder during take-off. Cessna’s and Pipers (amongst many others) need a tap of right rudder, the Tiger Moth, Chipmunk (at least if not re-engined) need a bit of pressure on the left rudder pedal to compensate. Light twin-engined aircraft for that reason have a “critical” engine, if that one fails control will be a bit more difficult than during a failure of the other one. Light twin-engined aircraft often do not have a lot of excess power to cope with an engine failure. A rather sick joke is: What is the purpose of the second engine on a light twin ?
Answer: If one fails, the other one will carry you to the scene of the accident .
If this still does not put you off flying:
To answer the original question: The banner is attached to the tail of the aircraft, I have in my original essay mentioned the grapnel with a line of 30 – 40 feet. But the banner itself is attached to a wide loop and between loop and banner is another line, also of 30-40 feet.
That brings the banner some 70 feet behind the aircraft – at least, which will move at about 50 – 60 mph through the air so the so-called “propwash” will not have much effect on the banner any more.
Then, because of it’s own weight and drag, it tends to hang maybe 10 – 15 feet below the height of the aircraft itself, bringing it out of the propwash anyway.
So the main concern is to ensure that it will hang straight, not flat or upside-down.
This is achieved by attaching the tow line to three lines (it gets complicated !) that in turn are attached to the front boom. The top line is the shortest, the middle a bit longer and the bottom one, of course, the longest. This brings the centre of gravity below the centre-line of the banner.
To further improve stability sometimes a small weight is attached to the bottom of the boom.
It will be evident that the banner itself will have to be well-made. Any stresses can cause the banner to twist in the airstream.
If it does rotate, it will more likely be caused by an aerodynamic fault in the banner itself than due to the propwash (the rotating air thrown back by the propeller).
Now, it the aircraft were to lose the banner or if e.g. an engine problem would require a premature jettisoning of the banner, the front boom will tend to fall straight down like a spear.
Some aviation authorities require the insertion of a parachute in the towing line in order to prevent serious accidents if the banner were to fall in a residential area. During flight, the ‘chute will be kept closed by the airstream, but in fall it will open. Of course, it is the duty of the pilot to include essentials like this in a pre-flight check.Especially in the case of newly made-up banners I have made it a point to go in the field with the ground crew to check it all over. On one occasion, the ‘chute was attached the wrong way around and would have opened during pick-up.
Now many may wonder: Is banner-towing dangerous?
Well, I was a member of the Tiger Club, then at Redhill north of London Gatwick for many years.
On the instrument panel of every aircraft they had a little placard with the inscription: “All aircraft bite fools”.
It applies to all types of flying. Training and a certain level of self-discipline, adherence to established and proven safety procedures and above all: not to assume that experience will be a substitute.
If you do ignore this, you need luck !
I have logged about 22000 flying hours in total. Nearly 4000 were “banner towing”. I have flown single-seaters, biplanes, twins, business jets and airliners both turbo-props and jets.
I have had a few difficult moments – and not even that many, coming to think of it, but no accidents ! None ! And I flew from 1965 until 2009.
Flying Signs « Now I Know Archives said
[…] As seen in this video (but you will have to look closely), the plane flies toward a pair of uprights, dangling a hook about 25 feet behind. The sign is attached to a big loop, which itself lays across a pair of uprights. When the plane flies over the uprights, the hook grabs onto the loop, lifting it — and the sign — skyward. In order to pull off the maneuver, the plane needs to get rather close to the ground — sometimes, no more than 30 or 40 feet above the surface. While the whole process is risky (and there have beenterrible accidents), it really is the only option available. (For an excellent essay on the entire process, click here.) […]
Now I Know – Flying Signs said
[…] As seen in this video (but you will have to look closely), the plane flies toward a pair of uprights, dangling a hook about 25 feet behind. The sign is attached to a big loop, which itself lays across a pair of uprights. When the plane flies over the uprights, the hook grabs onto the loop, lifting it — and the sign — skyward. In order to pull off the maneuver, the plane needs to get rather close to the ground — sometimes, no more than 30 or 40 feet above the surface. While the whole process is risky (and there have been terrible accidents), it really is the only option available. (For an excellent essay on the entire process, click here.) […]
Rudy Jakma said
Read my previous comments: Banner towing is only dangerous if the pilot is not properly trained and / or insufficiently aware of the risks.
That does not apply to aviation alone.
One problem is that aerial advertising – “banner towing” – is not used much any more to promote or augment sales efforts.
The result is a lack of training and a lack of pilots with a solid experience in towing operations. When I started flying (in 1965 !) it was “big business”, especially on the continent. A major Dutch air charter company Martinair, now the main air cargo arm of KLM Royal Dutch Airlines, began with tethered balloons, followed by banner towing and grew into a major operator. The founder, Martin Schroder, kept the banner towing operation going for many years. Of course, nostalgia was not the main consideration: it made money.
In the heyday of the 1970’s, this company “Luchtreclame Nederland”, re-named “Reclamair”, owned 12 Piper Super Cub 150hp aircraft.
The chief pilot, a man called Gerrit Wesseling, kept close watch over the operation and the standard of competence of the pilots. Accidents did not occur under his stewardship. And the company logged thousands of hours every summer season.
Rudy Jakma said
Suffering from nostalgia or just reading this and watching a few photos and videos are awakening old memories ?
These videos , mentioned in the original entry, are great stuff.
The C150 (“OO TOW”) video clearly shows the chutes: one attached to the towing boom of the banner itself, a smaller one on the grapnel (you wouldn’t want that falling on your head from 1000 feet now, would you ?).
Another one shows a pick-up with a Piper Pawnee, a purpose-built agricultural airplane with shots from the cockpit and a camera attached to the strut on top of the wing. Vveerryy nnnniiiicccceeee indeed.
It also seems to indicated the tightening of rules and regulations over the years.
Because the Pawnee takes off from a runway, climbs rather high and turns around the airport for the actual pick-up run.
In our wild-west days we would’ nay bother. Often we would take-off, make a quick side-step, throw the hook out and pick up without even bothering to circle.
Or, if we did, assuming there was not a lot of other traffic, we made the turns so tight that it once prompted the aerodrome manager to comment: “I know that you are flying commercially and time is money, but would you please keep your traffic pattern outside the aerodrome boundary ?”
This aerodrome was a grass field of no more than about 700 x 700 metres.
But some summers I flew more than 500 hours – in one single season !
On one occasion the local aeroclub had a spot-landing competition.
They had laid out a square, 50×50 metres and had to (try to) land in that square. Many missed.
Then the banner-towing pilots returned from their mission. We spotted the square and tried our hand. To the disgust of the competitors, not one of us missed the spot and most even managed to stop in the square. But then, we flew every day the weather allowed. And here is the key: because we knew exactly what the aircraft could do and what we could do with it. With the decline of banner towing, that level of experience has declined as well.