Continued Flight Research Articles

Effects of distance flown on pilot decision making in continued flight into deteriorating weather conditions

Introduction: Continuing flight into adverse weather remains a significant problem in general aviation (GA) safety. A variety of experiential, cognitive, and motivational factors have been suggested as explanations. Previous research has shown that adverse weather accidents occur further into planned flights than other types of accident, suggesting that previous investment of time and effort might be a contributing factor. The aim of this study was to experimentally determine the effect of prior commitment on general aviation pilots’ decision-making and risk-taking in simulated VFR flights. Method: Thirty-six licensed pilots ‘flew’ two simulated flights designed to simulate an encounter with deteriorating coastal weather and a developing extensive cloud base underneath the aircraft as it crossed a mountain range. After making a decision to continue or discontinue the flight, pilots completed a range of risk perception, risk taking, and situational awareness measures. Results: Visual flight rules were violated in 42% of the flights. Prior commitment, in terms of distance already flown, led to an increased tendency to continue the flight into adverse weather in the coastal ‘scud running’ scenario. Continuing pilots perceived the risks differently and showed greater risk tolerance than others. These ‘bolder’ pilots also tended to be more active and better qualified than the others. Conclusions: There are undoubtedly multiple factors underlying any individual decision to continue or discontinue a flight. The willingness to tolerate a higher level of risk seems to be one such factor. This willingness can increase with time invested in the flight and also seems to be related to individual flight qualifications and experience. Practical Applications: All pilots might benefit from carefully structured simulator sessions designed to safely teach practical risk management strategies with clear and immediate feedback.

South Atlantic Bight – a final stop for Ruddy Turnstones migrating to the Arctic

Migratory stopover sites are of high conservation concern especially those sites where shorebirds concentrate in large numbers to acquire fat reserves to fuel continued flight to breeding grounds. Many shorebirds use only a few stopover sites during northward migration to Arctic breeding grounds, thus identifying important locations, migration chronology, and flight routes are priority research topics to inform effective management strategies. We examined Ruddy Turnstones (<em>Arenaria interpres</em>) route and timing to Arctic breeding grounds from an island in South Carolina in the heart of the South Atlantic Bight using the Motus Wildlife Tracking System. Ruddy Turnstones leaving South Carolina did not migrate northward up the Atlantic coast but migrated inland through the Great Lakes Basin. Most Ruddy Turnstones did not make a stop in the Great Lakes Basin, thus making South Carolina the last presumed stopover before reaching Arctic habitats. Like other shorebird migration studies, most of the Ruddy Turnstones made use of tailwinds at departure and ground speeds were positively correlated with tailwind support. Future conservation planning for Ruddy Turnstones must consider the varied migratory routes and strategies of this declining shorebird species. This research also demonstrates the usefulness of Motus for tracking the movement of smaller shorebirds and the potential for strategic expansion of the Motus network to understand their full life cycle.

METHODOLOGY FOR QUORUM CONTROL OF THE REDUNDANT IRS SIGNALS IN THE MAIN MODE OF THE CIVIL AIRCRAFT CONTROL SYSTEM

Modern civil aircraft control systems operate, as a rule, in two modes - main and standby. The main control mode provides full control functionality with appropriate limitation for the flight crew due to the presence of redundant signals from interacting systems (such as IRS, ADS etc.). The standby mode provides control of the main control surfaces, allowing to continued safe flight and landing, but loses most of the protective functions. The redundancy of signals from interacting systems and their monitoring makes it possible to avoid the loss of the main mode of the flight control system due to single failures. Monitoring of the signals of interacting three-channel systems is ensured mainly by voting quorum up to the second failure, which is not a practically improbable event in terms of CS-25. These methods include the method of calculating the average value and the method of calculating the median value of redundant signals. In this paper, we propose a technique for quoruming triple redundant systems that provides control up to the third failure. The technique consists in using a confidence parameter for each channel of the interacting system, depending directly on its previous values (ie, monitor by value history). The results show that the use of this methodology will reduce the probability of switching to a standby control mode by almost one order of magnitude (and becomes an almost improbable event), as well as improve economic performance by increasing the Minimum Equipment List.

Charting the Edges of Human Performance

In the Horizon 2020 funded Future Sky Safety programme, the Human Performance Envelope project pushed airline pilots to the edges of their performance in real-time cockpit simulations, by increasing stress and workload, and decreasing situation awareness. The aim was to find out how such factors interact, and to detect the edges of human performance where some form of automation support should be employed to ensure safe continued flight. A battery of measures was used, from behavioural to physiological (e.g. heart rate, eye tracking and pupil dilation), to monitoring pilot performance in real time. Several measures – e.g. heart rate, heart rate variability, eye tracking, cognitive walkthrough, and Human Machine Interface (HMI) usability analysis – proved to be useful and relatively robust in detecting performance degradation, and determining where changes in information presentation are required to better support pilot performance in challenging situations. These results led to proposed changes in a prototype future cockpit human-machine interface, which were subsequently validated in a final simulation. The results also informed the development of a ‘Smart-Vest’ that can be worn by pilots to monitor a range of signals linked to performance.

Medical Suspension in Female Army Rotary-Wing Aviators.

Female aviators with health conditions may face a variety of occupational impacts. Outcomes may include a waiver for continued flight or a permanent suspension, in which flight is no longer possible. The objective of this study is to determine the prevalence of medical diagnosis among female U.S. Army aviators over a ten year period and identify associations of clinical diagnoses leading to waiver or permanent suspension. This study was a secondary data analysis; data were retrieved on 1,282 female, rated aviator patients from an Army Aviation epidemiological database. The archival dataset was composed of a total of 6,856 cases between June 2005 and June 2015. Age ranged from 19 to 58 years. The data were examined in terms of raw ICD-9 diagnostic codes, grouped system diagnoses (diagnosis categories), and occupational consequence. Spearman's rho correlations were used to determine associations between diagnosis, waiver and permanent suspension. The leading diagnoses were pregnancy, normal delivery, and allergic rhinitis. The systems approach yielded pregnancy, orthopedic disorders, and spinal disorders as the leading diagnosis categories. Leading waivered conditions included spinal, psychiatric, and neurological disorders. In terms of permanent suspension, the leading cause was depression, followed by migraine and post-traumatic stress disorders. In almost all diagnostic groupings, the Spearman's rho correlation coefficients between age and diagnosis were positively related. However, age was not associated with negative occupational outcome (permanent suspension), generally. A variety of conditions negatively impact the health and occupational status of female aviators, with disparate occupational impacts. Prevalent conditions differed from those reported previously for all aviators in a predominantly male population. The absence of cardiovascular disease is a significant change from 20-30 years ago. Among all medical diagnoses, a minority are responsible for a greater occupational burden.

Failure Detection of Composites with Control System Corrective Response in Drone System Applications

The paper describes a novel method for the detection of damage in carbon composites as used in drone frames. When damage is detected a further novel corrective response is initiated in the quadcopter flight controller to switch from a four-arm control system to a three-arm control system. This is made possible as a symmetrical frame is utilized, which allows for a balanced weight distribution between both the undamaged quadcopter and the fallback tri-copter layout. The resulting work allows for continued flight where this was not previously possible. Further developing work includes improved flight stability with the aid of an underslung load model. This is beneficial to the quadcopter as a damaged arm attached to the main body by the motor wires behaves as an underslung load. The underslung load works are also transferable in a dual master and slave drone system where the master drone transports a smaller slave drone by a tether, which acts as an underslung load.

Inability to regain normal body mass despite extensive refuelling in great reed warblers following the trans-Sahara crossing during spring migration

Migratory birds wintering in Africa face the challenge of passing the Sahara desert with few opportunities to forage. During spring migration birds thus arrive in the Mediterranean area with very low energy reserves after crossing the desert. Since early arrival to the breeding grounds often is of importance to maximize reproductive success, finding stopover sites with good refuelling possibilities after the Saharan passage is of utmost importance. Here we report on extensive fuelling in the great reed warbler Acrocephalus arundinaceus on the south coast of Crete in spring, the first land that they encounter after crossing the Sahara desert and the Mediterranean Sea in this area. Birds were studied at a river mouth and due to an exceptional high recapture rate (45 and 51% in two successive years), we were able to get information about stopover behaviour in 56 individual great reed warblers during two spring seasons. The large proportion of trapped great reed warbler compared to other species and the large number of recaptures suggest that great reed warblers actively choose this area for stopover. They stayed on average 3–4 d, increased on average about 3.5 g in body mass and the average rate of body mass increase was 4.8% of lean body mass d–¹. Wing length affected the rate of increase and indicated that females have a slower increase than males. The results found show that great reed warblers at this site regularly deposit larger fuel loads than needed for one continued flight stage. The low body mass found in great reed warblers (also in birds with high fat scores) is a strong indication that birds staging at Anapodaris still had not been able to rebuild their structural tissue after the strenuous Sahara crossing, suggesting that rebuilding structural tissue may take longer time than previously thought.

회전익기 연료펌프 안전성 평가 분석

The system and components for aircraft are required the design data on which the safety requirements are properly reflected for their certification. This paper presents the procedure and results of a safety assessments analysis for the rotorcraft fuel pumps in oder to confirm and verify them. The fuel pumps design assessment must be performed, including a detailed failure analysis to identify all failures that will prevent continued safe flight or safe landing. In order to assess the fuel pumps design safety, not only system safety hazard analysis and but FTA(Fault Tree Analysis) for proofing the safety objective of the fuel pumps are performed. The results of the safety assessment for fuel pumps validate that no single failure or malfunction could result in catastrophic failure or critical accidents of the rotorcraft.

Effects of Headset, Flight Workload, Hearing Ability, and Communications Message Quality on Pilot Performance

This study was designed to determine the effects of hearing loss, aviation headset type, flight workload complexity, and communication signal quality on pilots' performance in an army rotary-wing flight simulator. To maintain flight status, army aviators who do not meet current audiometric standards require a hearing loss waiver, which is based on speech intelligibility in quiet conditions. Because hearing loss characteristics of hearing-impaired aviators can vary greatly, and because performance is likely also influenced by degree of flight workload and communication demand, it was expected that performance among hearing-impaired aviators would also vary. Participants were 20 army helicopter pilots. Pilots flew three flights in a full motion-based helicopter simulator,with a different headset configuration and varying flight workload levels and communication signal quality characterizing each flight. Objective flight performance parameters of heading, altitude, and airspeed deviation and air traffic control command read-backs were measured. Statistically significant results suggest that high levels of flight workload, especially in combination with poor communications signal quality, lead to deficits in flight performance and speech intelligibility. These results support a conclusion that factors other than hearing thresholds and speech intelligibility in quiet should be considered when evaluating helicopter pilots' flight safety. The results also support a recommendation that hearing-impaired pilots use assistive communication technology and not fly with strictly passive headsets. The combined effects of flight environment with individual hearing levels should be considered when making recommendations concerning continued aviation flight status and those concerning communications headsets used in high-noise cockpits.

A methodology to determine pre-crash fuel quantity from post-crash fire thermal damage to an aircraft structure

The cause of engine failure that resulted in a catastrophic crash of a twin turbo-jet commuter aircraft is sought. The US National Transportation Safety Board and aircraft manufacturer contend that the engines failed because the aircraft ran out of jet fuel. The aircraft operators are confident that there was adequate fuel and that some other process caused fuel starvation. There was a post-crash fire that caused substantial thermal destruction of aircraft structure. If the majority of fire damage could be attributed to the burning of jet fuel, then it would be likely that the fuel inventory, just prior to impact with the ground, was adequate for continued flight. Thus investigators would have to conclude that some other mechanism caused the fuel starvation. In this work, a methodology is presented to determine the amount of fuel necessary to cause the observed thermal damage on the aircraft structure. The methodology is based on the determination of the heat flux and burning rates from the associated jet fuel pool fire and a heat transfer analysis to obtain the time required to melt structural parts subjected to the resulting heat fluxes. For an Aluminum alloy member, 70 mm thick, the time to reach the melting temperature of the alloy (∼500° C) is almost 4 min. Fully developed jet fuel pool fires burn at a rate of ∼0.06 kg/m2s, thus, for a pool fire of 10 m2, the fuel burned would be ∼130 kg, which is equivalent to about 151.4 L (40 US liquid gallons) of fuel. This fuel quantity would have been more than sufficient for the aircraft to reach its destination. Moreover, the actual quantity of fuel burnt would have been substantially more because of the conservative assumptions made in the analysis.

Eye Tracking Analysis of the Effects of Experience and Training on Pilots' Ability to Identify Adverse Weather Conditions

Adverse weather remains one of the leading causes of fatal accidents in general aviation. A large portion of fatal weather accidents involve visual flight rules (VFR) pilots' continued flight into instrument meteorological conditions (IMC). This study aims to analyze the way experience and training affect pilots weather identification accuracy, response bias, and visual scanpaths. The study involved 60 participants divided into three experience groups: non-pilots, low-time pilots, and high-time pilots. Participants viewed a series of weather scenes and were asked to determine if the conditions allowed for VFR flight. Participants then completed WeatherWise, a cue-based training program, before viewing another group of weather images. While training failed to improve decision accuracy for any group, all groups showed a significant shift in bias towards not continuing flight after training. The eye tracking data showed many differences in visual scan behavior between experience groups and training conditions.

Eye Tracking Analysis of the Effects of Experience and Training on Pilots' Ability to Identify Adverse Weather Conditions

Adverse weather remains one of the leading causes of fatal accidents in general aviation. A large portion of fatal weather accidents involve visual flight rules (VFR) pilots' continued flight into instrument meteorological conditions (IMC). This study aims to analyze the way experience and training affect pilots weather identification accuracy, response bias, and visual scanpaths. The study involved 60 participants divided into three experience groups: non-pilots, low-time pilots, and high-time pilots. Participants viewed a series of weather scenes and were asked to determine if the conditions allowed for VFR flight. Participants then completed WeatherWise, a cue-based training program, before viewing another group of weather images. While training failed to improve decision accuracy for any group, all groups showed a significant shift in bias towards not continuing flight after training. The eye tracking data showed many differences in visual scan behavior between experience groups and training conditions.

Characteristics of alcohol-related fatal general aviation crashes

Background: The effects of alcohol on piloting performance have been studied extensively. Information describing alcohol-related aviation crashes, however, is scant. Methods: We developed a data system for fatally injured pilots in Maryland, New Mexico, and North Carolina by linking autopsy data from the state medical examiner offices and crash investigation reports from the National Transportation Safety Board. Alcohol-related crashes are defined as those in which the pilot had a blood alcohol concentration of 20 mg/dL or greater. Differences between alcohol- and non-alcohol-related crashes were assessed with regard to pilot characteristics, crash circumstances, and human factors. Results: The National Transportation Safety Board recorded 313 general aviation crashes fatal to the pilot in the three states between 1985 and 2000. Of these crashes, 255 (81%) were matched successfully with medical examiner records. Alcohol testing results were available for 233 of the fatally injured pilots. Of those tested for alcohol, 25 (11%) had blood alcohol concentrations ≥20 mg/dL (mean=75 ± 64 mg/dL). The majority of alcohol-related crashes (52%) occurred at night (7 p.m. to 6 a.m.), compared with 28% of other crashes ( P < 0.01). Alcohol-related crashes were significantly more likely than other crashes to have involved continued flight under visual flight rules (VFR) into instrument meteorological conditions (IMC) (32% versus 12%, P < 0.01), and flawed decisions (64% versus 41%, P = 0.03). Conclusions: Distinctive epidemiological patterns are exhibited in alcohol-related fatal general aviation crashes. Alcohol appears to play a particularly important role in crashes involving flight under VFR into IMC.

Optimal City-Center Takeoff Operation of Tiltrotor Aircraft in One Engine Failure

This paper investigates optimal tiltrotor flight trajectories and performance in vertical takeoff operations from a city-center heliport considering the possibility of one engine failure. A two-dimensional longitudinal rigid body model of a tiltrotor aircraft is used. Tiltrotor flights after engine failure in both continued takeoff and rejected takeoff are formulated as nonlinear optimal control problems that minimize the heliport size, subject to various constraints from safety considerations and tiltrotor performance limitations. These problems are parametrized via collocation into parameter optimization for numerical solutions. Extensive numerical solutions are obtained, and sensitivity analyses are conducted to examine effects of model parameter uncertainties. Optimization results indicate that the maximum gross weight capability of a tiltrotor in a vertical operation is determined by the need for safe landing in the event of a single engine failure. The height at which the decision for either continuing or rejecting the takeoff is made depends on the need to maintain sufficient height during the continued takeoff flight after an engine failure.

Asymptomatic coronary artery disease detection: Update 1996: A screening protocol using 16-lead high-resolution ECG, ultrafast CT, exercise testing, and radionuclear imaging

The authors have proposed a new four-step screening algorithm to detect asymptomatic coronary artery disease (CAD) in flight school candidates, cadets, and rated flyers of the Unites States Air Force (USAF). In step 1, the USAF Armstrong Laboratory (USAF/AL) risk profile and improved 16-lead high-resolution electrocardiogram/vectorcardiogram will be recorded at baseline. On routine follow-up evaluations, quantitative serial comparisons will be performed by the method of Kornreich. In step 2, beginning with flight school candidates and cadets, all three groups will be studied by the ultrafast computed tomograph (CT) protocol. Those candidates positive for coronary calcium will be studied by coronary angiography and ventriculography, and their eligibility for continued rated flight status will be determined by present criteria. In step 3, those candidates negative for coronary calcium by ultrafast CT will then be screened by the newly defined and improved high-sensitivity treadmill exercise test criteria. In step 4, candidates with a positive treadmill exercise test result, or who are also found in the upper quintile of the USAF/AL risk profile, wild also have exercise nuclear wall motion studies and perfusion scans. If these are abnormal and suggestive of myocardial ischemia, this subset will also be studied by heart catheterization and coronary angiography, and their eligibility for continued rated flight status will be determined by present criteria. The incidence of coronary calcium/no calcium for each degree of stenosis in the 6,000 flyers in each quintile was used to develop the following projections: (1) that more than 3 of 4 rated flyers with unsuspected CAD, and (2) more than 9 of 10 with severe flow-limiting CAD can be identified by these upgraded screening procedures. Evidence is herein presented that these enhancements will result in a major (5–8-fold) increase in case finding of this disease. Based on the estimate of four lost high-performance aircrafts per year from sudden incapacitation of the pilot due to CAD, when this four-step screen is fully operational, it can be expected to reduce the $80 million annual losses to the United States government from CAD by 85%, a savings of $68 million per year.

Strategies for recontacting a lost pheromone plume: casting and upwind flight in the male gypsy moth

Abstract. Gypsy moth (Lymantria dispar L., Lepidoptera: Lymantriidae) males flying upwind to high concentration pheromone sources had lower ground speeds, shorter crosswind reversal distances and higher turn rates than males flying upwind to low pheromone doses. Casting flight, crosswind flight with no net upwind movement after loss of pheromone contact, developed gradually and was similar in fashion for males initially flying to the three pheromone doses tested; after plume loss, males' flight in the upwind direction decreased from 6 cm turn‐1 to nearly 0 cm turn‐1 by their fifth turn (crosswind reversal). After plume loss, upwind displacement decreased, crosswind distances and inter‐turn duration increased. Ground speeds tended to increase after plume loss, but airspeeds decreased following loss of 10 and 100 ng plumes and remained constant after loss of 1 ng plumes. Latency to casting was c. 1 s as measured by cessation of upwind progress and by timing the first reversal leg that was down or crosswind after plume loss. Though these measures of casting were independent of pheromone concentration, they are means that mask the fact that about 40% of males, rather than cast crosswind after loss of the plume, continued to move upwind, with wider and temporally less regular crosswind reversals. Such continued movement upwind is in sharp contrast to previous descriptions of casting flight after loss of odour‐plume contact. In addition, some males engaged in ‘regressive’ casting, moving downwind after bouts of ‘typical’ casting. The value of casting and of the continued upwind flight after plume loss, both possible strategies for recontacting a pheromone plume, are discussed.

Community conservation in belize: Demography, resource use, and attitudes of participating landowners

Surveys of local population resource use and attitudes are essential to the success of tropical conservation projects aiming to promote sustainable development. The following is a report from a survey of landowners participating in a voluntary conservation program for the black howler monkey Alouatta pigra known as the Community Baboon Sanctuary (CBS) in Belize, Central America. Interviews revealed a variety of issues requiring consideration by CBS managers: continued urban flight may jeopardize community stability; hunting and agricultural production methods will require management to lessen impact on wildlife resources and habitat; protection of the black howler monkey is enthusiastically supported for a variety of non-economic reasons; a majority of respondents feel they have benefited from participation in the CBS, but showed diminished confidence in deriving direct economic benefit from increased tourism to the CBS when compared to benefits from tourism at local or national levels. The continued success of the CBS will depend on locally-driven sustainable resource use and agricultural development in addition to well-planned tourism development in order to foster conservation of biodiversity.

Migration and the Spatial Dynamics of an Aphid, Myzus persicae

During migration the spatial distribution of aphids must become diffuse because migration is dependent on the wind. Mortality during host finding is of the order of hundreds, possibly thousands to one and the subsequent capacity for reproduction, once a migrant is established, is correspondingly great, so that the numbers and distribution of aphids are perhaps more a function of distance travelled, efficiency of host-finding, and reproductive rates than of subsequent mortality. There has yet been no evidence of any resulting geographical pattern in the epidemiology of aphids, nor any field assessment of the relative contribution made by the environment and by the individual behaviour, either at morph or species level, to the ultimate spatial distribution of populations. It therefore remains to be seen if aphids such as Myzus persicae (Sulz.), which feed mainly on annual plants, are as effective in finding and exploiting their spatially mobile resources as their highly sophisticated resource-searching adaptations might lead one to expect (Kennedy & Stroyan 1959; Taylor 1965, 1975). There are three seasonal cycles of population growth and redistribution in Myzus persicae in Great Britain, in common with many other aphids, and there is a progressive seasonal change in the morphology of migrants, although this is less pronounced in anholocyclic populations (Woodford & Lerman 1974). The migratory behaviour may be supposed to cycle correspondingly (Shaw 1973a, b). Control of migrant production and migratoriness originates in the environment, acting in complex ways through differential, temperature-dependent, plant and aphid population growth rates which in turn affect plant condition and density-dependent contact between individuals. In addition, temperature and light thresholds for take-off (Dry & Taylor 1970), and for continued flight, limit the occasions when migration can occur (Berry & Taylor 1968) but when it does, distances of tens or even hundreds of kilometers are commonly expected (Johnson 1969). These distances could thus have seasonal cycles, differing between the three migrations because of differences in weather, population density and individual behaviour, and this could affect gradients of distribution and the subsequent exploitation of resources. When the aphid is host to a parasitic organism, such as a virus, the epidemiology of the parasite is even more difficult to analyse. The analytical problems stem largely from the vast scale of the movements of aphids and the difficulty of following them in flight, but also from the different dimensions involved in the analytical process. The controlling variables for change in the overall population of the parasite are usually arrived at by a temporal modelling approach, often involving some kind of regression analysis (Watson & Healey 1953; Varley & Gradwell 1960). In contrast, it is the spatial distribution of the plant host that conditions the movements of the vector, whilst the timing of migration and differential survival between migrations are determined directly or indirectly by the

FLIGHT ACTIVITY OF PLUSIA GAMMA IN THE LABORATORY

Aktograph experiments showed lowered light thresholds for flight during the first three days after emergence of adult moths. Maximum flight duration was also reached at the third day. These three days probably represent the time when migration would occur in wild insects.Migration of insects usually begins post tenerally so it should be possible to direct migratory behaviour (i.e. the tendency for continued flight) in young adults of each generation of a species that migrates. The flight behaviour of Plusia gamma L. was studied in the laboratory to test this possibility.RésuméACTIVITÉ DE VOL DE PLUSIA GAMMA AU LABORATOIREDes expériences utilisant un actographe ont montré une inhibition moins forte de la lumière sur le vol pendant les trois premiers jours suivant leur émergence. La durée maximum de vol est atteinte au 3ème jour. Il est suggéré que ces premiers trois jours de la vie imaginale pendant lesquels le papillon a tendance à voler de facon continue, correspondent à la période d'activiTÉ migratoire.

Light and Temperature Thresholds for Take-Off by Aphids

Migratory flights by aphids can begin only when weather, especially light and temperature, permits take-off. For example light and temperature thresholds for take-off restrict the flight of Aphisfabae leaving its host plant within the daylight hours (Johnson & Taylor 1957). Once airborne, the temperature thresholds for continued flight differ considerably from those for take-off (Cockbain 1961; Taylor 1963). Some species of aphid, notably Schizaphis graminum, have been repeatedly recorded as migrating long distances. Because of the time taken for such migration, aphids must fly for more than one period of daylight and several species, including S. graminum, have been sampled at 2000 ft (609 m) over Kansas during the night (Berry & Taylor 1968). Hence either flight must continue, or take-off occur, during the night when light and temperature are most likely to be limiting (Taylor 1965). There is little evidence about continued flight at very low light intensities (Halgren & Taylor 1968); we here consider whether nocturnal take-off can contribute to overnight flights. We measured light and temperature thresholds for take-off by several species of aphid, including Aphisfabae and Schizaphis graminum, to seek specific limiting values that may permit, or prevent, nocturnal take-off as a prelude to long distance migration. The experiments showed also that some alatae were unwilling to take flight a second time, no matter how short the first flight had been and that some did not take off, as expected, at the end of the teneral period (Taylor 1957). This complicates the presentation of the temperature thresholds and has led to a revision of the former view of migrant aphids discussed elsewhere (Shaw 1968a, b).