Schlagwort-Archive: General Aviation

Human Factors Effects of Electronic Conspicuity Devices in UK General Aviation

Mid-air collisions are a serious threat in general aviation. Pilots are responsible for visual separation through see-and-avoid, but sighting issues remain the most common cause of Airprox events. Electronic Conspicuity (EC) devices have recently become common in GA and offer a means of supporting see-and-avoid. This research project reviewed the current literature and used a wide-ranging survey supported by several live-flights using eyetrackers to investigate the human factors issues related to the current EC situation.

Over 2000 survey responses were received (three-quarters from pilots of fixed-wing GA aircraft <5700kg). About 85% reported using EC of some sort (over and above a standard transponder), many used two or more EC devices and there were seventy-nine different EC combinations in use by the sampled pilots. The overall mean chance of detecting and being detected was approximately 50% (based on the sample only) but highly variable across EC combinations. Due to limitations, the real figure is almost certainly lower. Nevertheless, pilots overestimate the probability by about 10 to 20%. They are generally more confident about being detected than about detecting others. Pilot estimates of probability were found to be unrelated to the calculated figures for their combinations. This indicates a low understanding of detection and detectability likelihoods. This was reinforced by pilot opinions of fellow pilots; suggesting only 50% of pilots understand their devices.

Not only do pilots overestimate the detection coverage of their EC, but many appear to use EC in a way that assumes complete coverage (despite knowing that it does not). On seeing an undetected aircraft, 43% admitted feeling negative emotions (including anger), suggesting an unconscious expectation of full coverage. Many pilots commented on the ‘false sense of security’ that EC can generate, and some comment on feelings of anxiety. Nevertheless, when asked if they believed their device had saved them from a near-miss/collision, three-fifths of those who answered believed it had done so at least once.

A deeper analysis found that pilots are integrating EC more widely into the overall flying management task. Many pilots appear to use EC tactically and strategically to act, usually beyond visual range, to reduce future threats. Furthermore, some pilots report situations that imply that EC is factored into some risk-based decision-making. Evidence of EC ‘reliance’ was also found, with some pilots saying they feel very uncomfortable flying without EC. The risk of this is clear where the probability of detecting other traffic on EC is only 50% on average.

The largest issue appears to be a distraction by EC. Themes include distraction from the operational task priorities, unrealistic searches for EC targets, interacting with the device itself, information ‘overload’, and ‘nuisance’ or too many audio alerts (especially in busy and critical areas). Another distraction-related theme was general ‘head-down operation’ and a deteriorating look-out habit. There is a concern about attention becoming systematically focused on EC as a normal part of the overall task.

The survey results suggested a paradox in terms of EC safety and usability: EC appears to be least effective and most deleterious to the task in flight phases and situations where the mid-air collision risk is highest (confirmed by the literature review), such as when in busy areas (circuits, busy airspace, thermals, etc). Pilots report EC being overwhelming and distracting in these situations and many will ignore it (‘cry wolf effect), switch it off, or even decide not to take it at all because of this. Hence in its current form EC is least effective (from a human factors perspective) in situations where it is most needed, and this will remain the case even if coverage and compatibility are substantially increased.

Live flying eye-tracking trials supported many elements of the analysis and uncovered several new themes. During trials, more non-EC visual targets were seen than aircraft showing on EC, confirming the compatibility problems. Visual lookout limitations were supported by eye tracking (E.g. thorough active lookout in the direction of a threatening aircraft (unknown and non-EC) for several minutes failed to see the aircraft at all, despite ideal good conditions. Examples of active lookout were mapped and compared to EC-cued-searching, demonstrating that EC-cued searching can restrict lookout considerably as emerged as a concern in the survey. Realistic visual range was confirmed to be about two miles, and up to three in perfect circumstances. The impact of a pilot conducting a visual search for an EC target well beyond the visual range was demonstrated to be a threat. Two trials showed examples of pilots resolving information from two aircraft (radio and EC) into one (a phenomenon termed ‘2-in-1’), and in one case concentrating on the EC aircraft at the expense of the other. Source / entire study: ‚GASCo and Jarvis Bagshaw Ltd.‚.

The Future of General Aviation Fuels

Schreibe eine Antwort

Currently, the two principal types of fuel used in Aviation are Avgas 100LL and Jet A-1; Jet A-1 for turbine engines and Avgas for spark ignition piston engines. If you are a general aviation pilot, the one you are probably more familiar with is Avgas and it is this which we will concentrate on here. As you may be aware, Avgas contains Tetra Ethyl Lead (TEL) – the additive which has recently been banned in automotive forecourt fuels in the European Union for environmental reasons. Although the total fuel volume used in aviation is less than 0.5% of that used in the automotive sector in Europe, there is considerable pressure from Environmental Lobbyists to remove or replace TEL in Avgas and produce an unleaded grade. To understand what is involved, we first need to look at what benefits TEL has. As you may know from the problems with Automotive fuels, Lead compounds from TEL form a protective layer on the valve seat and prevents the soft valve seats from eroding. Without TEL small areas of a soft metal valve seat will fuse to the valve and be ‚plucked‘ from the face of the seat.

Once attached to the valve they form an abrasive surface which further damages the valve seat. This combination of actions is known as Valve Seat Recession (VSR) as the seat of the valve is worn away and recesses into the cylinder head. The solutions to this are to either use a VSR additive or fit hardened valve seats which are resistant to this action. VSR additives are now commonly used in Lead Replacement Petrol on automotive forecourts, however for several reasons they are not yet approved for use in aviation engines. This means that the only current method of preventing the Valve Seat Recession for aviation engines using unleaded fuels would be to fit hardened valve seats. This is common in new manufacture Avco Lycoming and Teledyne Continental engines, but some older engines would need modification.

The other more significant problem with unleaded fuels is that of Octane rating. Octane rating is a measure of how resistant a fuel is to detonation or „pinking“; the higher the Octane rating, the more the fuel/air mixture can be compressed without detonation happening. To make this clear, octane rating is not a measure of the amount of energy in the fuel but is a measure of its resistance to detonation. The advantage of higher octane fuels is that a higher compression ratio or supercharging ratio can be used, which then leads to a higher engine cycle efficiency, which in turn means more power output for a given fuel burn. However, to confuse things further, there are four principal ways to measure Octane rating, RON, MON, Lean Mixture and Rich Mixture ratings. Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 – 98 RON but are only 85 – 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating.

The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitudes, for example during take-off. As you can see TEL in Avgas makes a significant difference to the octane rating and without it, Octane ratings would be back down to 80 – 85 Lean Mixture – the level for road fuels – instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 – 85 Lean Mixture Octane fuel. However, for those aeroplanes with supercharged or turbocharged engines, the use of low octane unleaded fuels would not be suitable. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the supercharging and massively de-rate the engines. This de-rating would be so severe that many of the engines would no longer be powerful enough for the aeroplane in question. Modern aviation unleaded fuels are currently being developed, such as 82UL in the United States. This is an 82 Octane Lean Mixture rating fuel and is approved for use in modern non-turbo Avco Lycomings engines amongst others. However, it is not yet available in Europe but also not everyone can use it – your aircraft manufacturer must raise an Aircraft Modification document to approve its use. Some new Cessnas are approved to use 82UL, but most aircraft types currently do not have the manufacturer’s approval. The potential quantity of Avgas piston-engined aircraft worldwide that could use this grade is estimated to be around 60%, although some of these would probably need fuel system modifications prior to approval.

To date, there are no additives available to replace TEL which increase the Octane rating – the additives used in automotive Lead Replacement Fuels only tackle the problem of valve seat recession and do not effect the Octane rating of the fuel. Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer to raise a modification to replace their engine with either a turboprop or diesel engine. This brings us to the other recent advance in General Aviation engines; the development by several engine manufacturers of diesel engine technology. Shell is involved with all of the major prospective aviation diesel engine manufacturers and is working closely on these projects. These engines potentially offer several significant advantages over Avgas engines. They return up to 30% better fuel economy, use Jet A-1 rather than Avgas, and have the potential to be retrofitted to many light aircraft, replacing their current Avgas type engines. The downside will be the cost of engine replacement and aircraft modification and whilst some applications may be able to take advantage of this technology, this will not be a solution for everyone. So in summary, Aviation engines present many unique challenges to the development of Avgas and as such, there is yet no firm date to replace Avgas 100LL, but there can be little doubt that eventually Leaded Avgas will be withdrawn from use. However, this does not seem likely until suitable fully developed alternatives are available; a situation that is likely to be several years into the future. Source: ‚Shell‚. Bild: ‚Continental‚.

Mit kleinen Fliegern an große Flughäfen

Schreibe eine Antwort

Einmal in Frankfurt oder Heathrow landen und zwischen großen Jets rollen. Das ist der Traum vieler Privatpiloten. Ist das möglich? Wenn wir als Gäste am Flughafen sitzen und aus den großen Glasfenstern schauen, sehen wir eher einen Airbus A380 als eine kleine Cessna 172. Tatsächlich ist die Entdeckung eines kleinen Privatflugzeuges an großen Airports aber realistischer, als wir denken. Doch wer als Privatpilot an einem Drehkreuz landen will, für den gibt es einen Haken: die Kosten. Es gibt durchaus einige größere Flughäfen, wo es nicht nur Spaß macht, zu landen, sondern auch Sinn – etwa weil es einen schnellen Anschluss an die Stadt gibt. Der Stuttgarter Flughafen ist einer davon, aber auch Friedrichshafen, Kassel oder Sylt sind sehr spannend. Betrachtet man die durchschnittliche Landegebühr von rund 10 bis 50 Euro für eine typische Cessna 172, so ist es auch erschwinglich. Dann gibt es aber auch Flughäfen wie Frankfurt. Manch ein Pilot träumt davon. Es ist tatsächlich eine einmalige Erfahrung, zwischen den riesigen Maschinen zu rollen und sich fast ebenbürtig zu fühlen. Aber lohnen sich dafür Kosten im oberen, dreistelligen Euro-Bereich? Diese Frage muss jeder Pilot für sich selber beantworten. Eines ist sicher: möglich ist es. Möchte man die Erfahrung machen, aber nicht ganz so viel ausgeben, so lohnen sich eher kleinere, aber dennoch internationale Flughäfen wie Düsseldorf, Köln oder Berlin-Tegel. Und wer die Kosten scheut: warum den Flughafen anfliegen, wenn man auch einfach über ihn hinweg fliegen kann? Das sogenannte Midfield Crossing, wie der Name schon sagt, ist eine Praxis, die viele Piloten nutzen, um sich das Leben eines Flughafens mal von oben anzusehen. Hier wird ein Überflug in sicherer Höhe quer über den Platz durchgeführt. Aber Achtung: auch das ist nicht einfach so möglich. Solch ein Überfliegen muss in jedem Fall vom Kontrollturm genehmigt werden. Oft passiert es, dass die Anfrage abgelehnt wird. Manchmal ist eben einfach zu viel los. Das muss man akzeptieren und damit leben. Wo dieses Crossing am meisten Spaß macht? In London-Heathrow. Je nach Tageszeit erlauben die Lotsen einem hier den Überflug am Anfang der Piste 27L im Osten. Eine geniale und zugleich einmalige Erfahrung. Quelle: ‚aerotelegraph.com‚.