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CHAPTER 2 TECHNICAL AND TECHNICAL ASPECTS OF OPERATIONS

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Contents


          Para      Subject

          2.1       Daily Inspections
          2.2       Recording of Defects
          2.3       Fuel
          2.4       Oil
          2.5       Tug Hangar and Fuel Pump Keys
          2.6       Moving aircraft by hand & Putting aircraft away
          2.7       Ropes
          2.8       Moving the Prop by Hand
          2.9       Washing aircraft - windscreens & airframes
          2.10      Counters for engine running time
          2.11      Flight Manual Limitations
          2.12      Engine Costs

          TECHNICAL ASPECTS OF TUG OPERATIONS

          2.13      Cold Starts
          2.14      Radio in Tugs - Useful Frequencies (Table)
          2.15      Warming Up
          2.16      Run Ups - Live Mags, etc
          2.17      Takeoff
          2.18      Climb
          2.19      Red  Operating rpm Band on Lycoming 180 hp Engines
          2.20      Action if an Engine Overheats
          2.21      Release - Critical Engine Handling
          2.22      What to do if you have an accident


This chapter contains material which concerns technical aspects, including maintenance, replenishment, turnround, and some aspects of flying operations which have a substantial technical or engineering bearing, such as engine handling after release, and overheating during the climb.

2.1 DAILY INSPECTION / CHECK A. Amendments to the Air Navigation Order (ANO) have made the DI a mandatory part of the maintenance schedules that exist for all aircraft. It is called the CHECK A. These Checks, which tug pilots are entitled and expected to do, also have to be recorded and signed for in a DI Book kept in the aeroplane. Treat each DI as though you know there is a fault in the aircraft and your life depends on finding it. Over the years people have found fuel leaks, live magnetos, excess play in tailplanes, loose flap guides, undercarriage problems, structural cracks etc that could well have lead to an accident had they not been detected. The Annexes include a guide for the DI of each type.

2.2 RECORDING OF DEFECTS. If an aircraft develops a defect, first write details of the defect on the aircraft's tug log sheet and put a more detailed account in the DI Book. Use words that will be easily understood by other pilots and hangar staff, words are cheap, misunderstandings are not. `Flaps U/S' is not an adequate description, it could mean one of many defects; describe the symptoms in detail. During midweek working hours take the aircraft to the tug hangar, unless the defect is minor, tows are needed, and there is no replacement tug. The hangar staff may be able to fix the defect quickly. Outside hangar working hours, if the defect is such that the aircraft is safe to fly, brief the next pilot on handover. If the defect makes the tug unsafe to fly, ensure an additional obvious notice is put in the cockpit (the log sheet will eventually be taken back to the office so you can't depend on that), inform a senior staff member (Manager, CFI, DCFI, Tugmaster) and finally put the tug into or outside the tug hangar ready for repair. Do not leave this for someone else to do, safety depends on you acting responsibly. The essence is that there should be no possibility of another pilot climbing in and flying the tug in ignorance of the defect that you have found. After weekend operations, the Staff tug pilot or the Manager will check all DI books on a Monday morning, and action any snags.

2.3 REFUELLING. When taxying up to the pump, ensure you do not blow stones into the tug hangar and pull the tug towards the peritrack before restarting it if the hangar doors are open. The hangar staff get very narked if you blow stones and dust at them, in addition they may have covers and cowlings off and the debris could do real damage to another aircraft. At another site an accident occurred when a car passing behind a tug being refuelled caught the rope and pulled the aircraft into the fuel pump. To avoid a similar incident at Lasham pilots must pull the rope clear of the peritrack as soon as they are out of the aircraft. Also, with tailwheel aircraft such as the Super Cub, the rope can get caught in the tailwheel assembly when you are turning the aircraft by hand before taxying away; if this happens and you don't notice it, the first evidence may be a loss of directional control when taxying; if you've put a lot of power on you could taxy into something before you can stop.

2.4 OIL. Every time a tug is refuelled, the oil must be checked. If oil is needed and the fuel pump and shed are locked, walk back to the Clubhouse to get the key anyway, do not risk a ruining a £12,000 engine just to save time or a walk. Ensure the dipstick is not allowed in contact with any dirt whilst topping up the engine, and always wipe it before putting it back into the engine. Do not overtighten the oil filler cap, firm hand tightening is all that is needed. Other than for running-in a new or refurbished engine, we use Aeroshell 80W or 100 oil. It is kept in the wooden hut in a 50 gallon drum with a hand pump screwed into the top.

2.5 KEYS - TUG HANGAR, FUEL PUMP AND OIL STORE. The Tug Hangar, Oil Store and Fuel Pump must be locked up overnight. We assign responsibility to see this is done to the last person to fly a tug on the day, but other pilots around at dusk should also check everything really is locked up. The fuel pump keys are hung as one bunch in the Parachute room; in the morning, as soon as the locks have been undone, return the keys to the Clubhouse. The oil store is presently secured with a combination padlock, the fuel pump by a conventional padlock. DO NOT LEAVE THIS KEY IN THE OIL STORE. The tug hangar key may be obtained if required from a staff member. When locking the tug hangar, please make sure that each door is bolted and all the chains are in place.

2.6 MOVING AIRCRAFT BY HAND. Care must be taken in moving aircraft by hand, not only so that they are not pushed into things or damaged by people pushing on the wrong places, but also the PROPS MUST ALWAYS BE TREATED AS LIVE EVEN THOUGH THE SWITCHES ARE OFF. It is better to push on the wing tips or fuselage than pull on the prop, only do the latter as a last resort and make sure that it does not turn. See also para 2.8 on live mags. In the case of Regents, the nosewheel handle is not held in by a pin as it is with Rallyes; be careful if you are pulling hard on a Regent handle, if it comes out of the nosewheel fitting you may fall heavily on your back. Aircraft must be pulled clear of the stony ground before starting, since stones damage props and repairs are expensive.

2.7 AEROTOW ROPES. A complete rope costs £45 as we go to print, so we need to take care of them. New tow ropes are made up by the staff as necessary and there should be two ropes in each tug and a spare in the launch point control van. Tug pilots are expected to monitor the ropes in use, and ensure that knots, worn ends, are cut out and re-spliced so that ropes are always safe and yet are not discarded before they need be. Tuition in splicing may be had from the flying staff or the tugmaster! Any ropes considered unserviceable should be returned to the office with a note attached so that it can be checked by the staff before it is `retired'.

2.8 MOVING THE PROPELLER BY HAND. The vital rule is: Always treat propellers as live all the time or you may be maimed or killed. Over the years at Lasham we have had several occasions when engines have been found to have live ignition with both switches off, due to faults in the ignition switches or other parts of the ignition circuit. Remember that all aero engines are designed so that the ignition fails live. Unlike your car, if a tug's ignition switch is faulty it may be LIVE when it's showing OFF. At Lasham, we have had engines fire with both mag switches off and the prop being turned slowly, resulting in one serious injury and some frightening near misses. Perhaps people survived the near misses because they were remembering the rule! As an example, some years ago, a wire came off one mag switch in a Lasham tug and the engine fired as the prop was being turned during the DI. This could occur with any engine however slowly the prop is turned, because the impulse mechanism in the left mag is there to ensure this can happen. Shortly after this incident, we also found a live mag in another tug, due to a fault within an ignition switch. It was no co-incidence that both faults were found by the same tug pilot, who habitually checked for live mags as well as for mag drop. See para 2.8 and para 16.1 on live mags.

2.9 WASHING - WINDSCREENS AND AIRFRAMES. Flying with dirty windscreens in the crowded skies around Lasham increases the risk of a midair collision, particularly if flying into-sun. Tugs must not be flown with dirty windscreens, and if a pilot needs to stop to clean the windscreen, he should do so regardless of the length of the queue. All tug windscreens are easily scratched Perspex (Plexiglass plastic) and ideally should only be cleaned with Perspex cleaner. Experience with silicone based spray polishes such as Sparkle or Pledge has shown that provided the spray is first spread gently over the screen and allowed a brief time to soak into the dirt then they are very effective provided they are polished off with a clean cloth. Silicone-based polishes are not allowed on aluminium so keep them off the rest of the aircraft. Pilots should also volunteer to clean the tugs as often as possible. Dirt, insects, and exhaust emissions all degrade the performance of the tug and increase the effects of corrosion. Hoses have been provided at the fuel pump and outside the main hangar specifically for washing tugs.

2.10 COUNTERS FOR ENGINE RUNNING TIME. Record the engine counter reading shown in the middle of the rpm gauge at the start and end of each day's flying on the aircraft's log sheet. If any cross country flying is done, note the start and finish counter readings. The counter readings are a great help sorting missing or other problem log sheets. They are important, please fill them in.

2.11 FLIGHT MANUAL LIMITATIONS. Advice, recommended practices, and legal requirements are to be found mixed together in the various publications relevant to towing. Documents such as the Air Navigation Order (Sect 37), Civil Aviation Publication 393 (CAP 393), CAA and BGA Information Circulars, BGA Laws and Rules and the Aircraft Flight Manual all contain valuable information some of which is mandatory either to the conduct of the flight or the maintenance of the aircraft and its equipment. Unfortunately, some of the information does not agree with others. As an example, Rallyes have a different placarded maximum towing weight to the one given in the Flight Manual. Whenever possible, stick to the Flight Manual as the manual is part of the Certificate of Airworthiness and is approved by the CAA. The aircraft must be operated within the limitations given in the Flight Manual (ie airframe & engine limitations such as Vne, Vra, Vm, Vflap, Vmin tow, rpm, oil temp/pressure, CHT etc) for the C of A and therefore the Insurance to be valid (unless the exceedance of a given limit was caused by a plausible course of action following a malfunction or emergency).

2.12 ENGINE COSTS. At the time of printing, a Lycoming 180 hp engine cost £12,000 to buy new or £9,500 to overhaul an existing engine. At Lasham we have only ever had two engines go past 2000 hours without needing cylinder repairs, in 2144 hours in G-BLGS from 78 to 83, and 2800 hours in G-BJUD up to the time of printing. Often the cost of the repairs reaches £2000 as a cylinder costs £1000 and a piston without rings £450. With sums as large as these involved it is obviously vital pilots take the utmost care of their engines from start up to shutdown.

TECHNICAL ASPECTS OF OPERATIONS

2.13 COLD STARTS. The following applies to the first start of the day all year and to every start when the engine is cold during the winter months. Before turning the engine over with the starter, pilots should give 4 primes on the throttle and then, taking the precautions listed in para 2.8.1, turn the engine over at least 4 compressions by hand. Turning the engine over will check for hydraulic locks and good compressions, it will also circulate the oil and draw in some mixture to aid starting.

2.14 RADIOS IN TUGS. Radio switches and controls are deliberately small for low weight and minimal space requirements, so operate them gently - we have had some pulled off! Inevitably their small size makes these controls easily broken and vulnerable to mishandling. The radios are designed for aircraft use and so should be OK to be on during start up and shut down, after all, at some airfields you have to ask Air Traffic for start clearance and you can't do this without radio! However, some people say that radios last longer if you turn them off during engine start and stopping since the aircraft electrical system may produce an uneven voltage while the alternator runs up or down; at Lasham there is no evidence either way so it's your choice. Pilots without R/T Licences are reminded that they should be working for one, and no new tug pilots will be accepted unless they have an R/T Licence. The radios are a big help in retrieves, especially into airfields, and across zones. If you are restricted to the BGA frequencies, ie by not having an R/T licence, and are unable to talk to Air Traffic, you are likely to be increasingly restricted to flying at Lasham only.

USEFUL RADIO FREQUENCIES (MHz, listed in numerical order)

2.15 WARMING UP. As soon as an engine responds to the throttle and the oil pressure is satisfactory, ie not too high and not too low, the aircraft can be taxied onto the airfield ready to run up. It may seem surprising but it is actually bad practice to try too hard to `warm up' an aircooled engine (liquid cooled engines are different). In their engine manuals, Lycoming stress that adequate cooling and even cylinder temperatures are only provided by the forward speed of the aircraft and that ground running should be kept to a minimum using only a maximum of 1000 to 1200 RPM. Lycoming also suggest taking off as soon as the engine responds to the throttle without faltering, rather than waiting for a set oil temperature on the gauge. The reason for this advice is to avoid local hot spots developing in cylinder walls that can wear the cylinder and its piston. In practice this means that, at normal ambient temperatures, an aircraft that has been taxied out and run up is going to be warm enough for take off. It does not mean that in the dead of winter you can take off safely straight away, use common sense and when it's cold, warm the engine for longer. Where an aircraft has stood alongside the aerotow point, run it at 1000-1200 RPM until the oil temp is obviously rising and the CHT nearing 125°C before commencing a take off; idling rpm is too low as it can cause plug oiling. The higher rpm gets the fuel flowing through the carburettor and also avoids any tendency for a `rich cut' on takeoff due to overfuelling as you go to full power.

2.16 ENGINE RUN UPS. Position the aircraft on the airfield on short grass well away from any stones. Check the nose is into wind to aid cooling, make sure that the propwash will not affect anyone else, and check that the way ahead is clear just in case the brakes fail. Check the mags at 1800 RPM on 180HP engines. Ensure there is both a mag drop and a recovery to the original rpm.

2.17 TAKEOFF. Do not just ram the throttle fully forward, advance it forward gradually taking about 3-4 seconds to apply full power. During the ground run check for good oil pressure and expected RPM. With a fixed-pitch prop, rpm at a given speed equates to power.

2.18 CLIMB. Climbs while towing should normally be carried out at full throttle. The engine has a full power mixture enrichment jet that provides an over-rich mixture to help cool the exhaust valves, this is brought into use by the last 10% of the throttle movement and there is the danger that if you reduce power you may shut this jet off, making things worse for the engine. Lycoming say there is no advantage in climbing at reduced power. The enrichment jet also greatly reduces the possibility of carburettor icing while it is in operation; some say it eliminates it but in severe icing conditions there must be a possibility of it occurring, at least upstream of the point at which the enriched mixture is injected into the carb venturi. Monitor the CHT, which must not exceed 260°C (500°F). The oil temp must also be watched carefully, it must not exceed 118°C (245°F), see para 2.20. As oil is progressively overheated, it loses a lot of its lubricating qualities and engine bearings can be damaged. Use of the mixture control to lean the mixture is not normally recommended above 75% power. However when doing a high or long tow it is acceptable to lean an engine even at full throttle just sufficiently to restore smooth running, but this should not be necessary below 4000 ft. Do not attempt to lean an engine to gain extra RPM.

2.19 THE RED OPERATING BAND ON 180 HP ENGINES. The Lycoming 180HP Engine comes in many versions, each of which can be fitted with a variety of different propellers Unfortunately tests and bitter experience have shown that certain combinations of engines and propellers interact between 2150 and 2350 RPM. This interaction is caused by the engine being a high compression design with 4 big cylinders; each firing stroke transmits a healthy punch to the crankshaft which flexes in torsion and develops a significant torsional vibration in the speed range quoted. This vibration is picked up by the propeller which translates it into a point of maximum vibration about 10 inches in from the propeller tip, this has caused the fatigue failure and loss of individual blade tips in flight resulting in severe engine vibration, emergency engine shutdowns and forced landings into fields. The engine/propeller combination most at risk is the hollow crankshaft A2A and A3A series engines fitted with a fixed pitch metal propeller. Fortunately at Lasham we have pursued a policy of solid crank A3A and A4A engines, and wooden four-blade propellers. At the time of printing, there is no red band restriction on any of our tugs. However most other clubs still operate the hollow cranks, so be aware if we have a visiting tug on site.

2.20 ACTIONS IF AN ENGINE OVERHEATS. In hot weather, the tug pilot may notice either the cylinder head temperature or the oil temperature reaching the red line. If this happens, speed up the tow by 5 to 10 Knots. If this fails to halt the temperature rise try reducing rpm by 50-100 and if this fails, wave off the glider and land. After landing, check the following:

2.21 AFTER RELEASE - ENGINE HANDLING. Careful and correct engine handling during this phase of flight is absolutely critical. If one pilot out of our total numbers starts doing it wrong then he will wreck an engine on his own, it is essential no one thinks he can do it his way and it will not matter because everyone else is handling it correctly. The problem facing the pilot is how to cool the cylinders slowly because if he simply closes the throttle at the end of the climb and pushes the nose down increasing the airspeed before long he will crack a cylinder.

2.22 WHAT TO DO IF YOU HAVE AN ACCIDENT. If a tug is damaged in your charge you are considered responsible and you must not continue to fly tugs until given authorization to do so by the Tugmaster, the CFI, DCFI or the Manager. Similarly if a glider is involved in an accident where the outcome was, or could have been, affected by the actions of the tug pilot that pilot should also check with the CFI etc that he can continue towing. Report the incident at once to the Tugmaster, CFI, DCFI or Manager who may well require a written statement of the event. In accidents involving serious damage or personal injury the aircraft must not be moved without permission from the CAA, the Manager or CFI will contact them. In less serious cases, move the aircraft into or outside the tug hangar, writing up the defect or damage in the normal way in the DI book, log sheet, and on an additional notice in the cockpit so that another pilot does not inadvertently fly the aircraft in ignorance of the defect or damage.

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Last updated by John Leibacher on Sunday, November 5, 1995 at 17:47


Dr. Günther Eichhorn
Springer 233 Spring Street New York, NY 10013 USA, email me