Federal Aviation Administration's National Research Articles

Comparative Performance of Different Warm Mix Asphalt Technologies under the Influence of High Aircraft Tire Pressure and Temperature

Warm mix asphalt (WMA) technologies allow the production and placement of asphalt concrete materials at a lower temperature than the traditional hot mix asphalt (HMA). These materials simultaneously reduce the production fuel costs, increase the available hauling distance, lengthen the paving season, are eco-friendly, and ensure safer working conditions. Airport authorities can use such materials for construction applications to minimize the downtime and user-delay costs. However, the existing Federal Aviation Administration (FAA) construction specifications do not provide guidance on the implementation of such technologies, especially under the conditions created by aircraft with high tire pressure. To this end, the FAA National Airport Pavement and Materials Research Center (NAPMRC) conducted accelerated pavement tests as part of Test Cycle 1 (TC-1) to study the application potential of WMA (using chemical additive) on airport pavements. TC-1 results showed WMA performance was comparable to P-401 HMA performance in rutting. Test Cycle 2 (TC-2) study investigated the rutting performance of chemical, organic, and hybrid additive-based warm mixes alongside an FAA specification P-401 HMA counterpart. Four different test lanes were constructed accordingly in the outdoor area of NAPMRC, each encompassing three different test sections. Using the sixth-generation airport heavy vehicle simulator (HVS-A), sections on the north side of the test lanes were trafficked with 61.3 kips (272.7 kN) moving wheel load at a controlled temperature of 120°F (48.9°C). The chemical additive-based warm mix appeared to exhibit comparable performance to the HMA. A laboratory characterization effort also seemed to corroborate the rutting observations from traffic tests.

Assessing Owl Collisions with US Civil and US Air Force Aircraft

Collisions between wildlife and aircraft (wildlife strikes) pose notable risks. Previous research has found that a variety of birds and mammals are involved in wildlife strikes, but no comprehensive evaluation of collisions between owl and aircraft (owl strikes) has been conducted. We queried the Federal Aviation Administration's National Wildlife Strike Database (from 1 January 1990 to 30 June 2014) and the US Air Force's Birdstrike Database (from 1 January 1994 to 30 June 2014) to characterize owl strikes. We found 2531 owl strikes involving at least 20 species of owls. Barn Owls (Tyto alba) were the most frequently struck species, accounting for 42% of all reported owl strikes. Almost 75% of owl strikes occurred during the night. Owl strikes typically occurred within the airfield environment itself, and 86% of owl strikes occurred when the aircraft was at or below 30 m above ground level. Some mitigation tools and techniques (e.g., nonlethal hazing, translocation, lethal removal) can reduce the frequency of owl strikes, but the efficacy of these methods remains unevaluated. An important area of future research will involve the development and evaluation of effective, publicly acceptable methods of reducing human–owl conflicts.

Full-scale test of thermally induced reflective cracking in airport pavements

While a reflective cracking propagation rate of 25 mm per year is well accepted by airport pavement engineers, the mechanism of reflective cracking under field conditions has not been fully investigated. A recently completed project sponsored by the Federal Aviation Administration (FAA) led to the development of the Temperature Effect Simulation System (TESS). After an in-depth evaluation of the TESS, full-scale tests to mechanically simulate thermally induced reflective cracking were conducted. A large simulation matrix was first developed to select promising joint opening and displacement rates using three-dimensional viscoelastic-based finite element analyses. A test pavement was then built, instrumented, and tested at the FAA National Airport Pavement Test Facility (NAPTF). This paper describes the successful full-scale test, crack monitoring under accelerated loading, and the data analysis used to evaluate the crack development. Main research conclusions included: (1) “25 mm per year” was quite conservative for thermally induced reflective cracking; (2) Once bottom-up reflection cracks reached a critical length, the crack evolution became very aggressive. For that reason, it is hypothetical to sandwich a strain-relieving hot mix asphalt interlayer between the Portland cement concrete slabs and the new overlay to minimise overlay stresses and to tolerate horizontal movements at the joint. Furthermore, significant insights into the mechanisms and mitigation of thermally induced reflective cracking were obtained and presented. Findings from this study are of immediate assistance to airports supporting light to medium weight aircraft and experiencing significant temperature cycling.

Forensic investigation of failed airfield test pavements

Field and laboratory forensic studies were conducted to investigate the failure mechanisms of four different flexible test pavement sections at the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF), a state-of-the-art full scale pavement test facility dedicated solely to airport pavement research. The first set of test pavements constructed at the NAPTF included a total of nine test sections (six flexible and three rigid) built on three different subgrade materials: low-strength, mediumstrength, and high-strength. All test sections, except the high-strength test sections, were subjected to simulated repeated aircraft loading until the test sections were deemed to be failed. After the completion of traffic testing, trenches were dug in each of the flexible test sections to conduct post-traffic investigations into the failure mechanism of the pavement structures. Forensic tests conducted on the pavement component layers during trenching included CBR, in situ densities and moisture contents, and Dynamic Cone Penetrometer (DCP) tests. Heavy Weight Deflectometer (HWD) tests were conducted on the test sections before the trenches were dug. This paper focuses on trench investigations conducted on low-strength subgrade test sections. In the low-strength subgrade test sections, rutting was observed in the AC layer, unbound base and subbase layers in both the traffic paths. Shoving occurred in the AC layer.

Airfield pavement deterioration assessment using stress-dependent neural network models

In this study, an artificial neural network (ANN)-based approach was employed to backcalculate the asphalt concrete and non-linear stress-dependent subgrade moduli from non-destructive test (NDT) data acquired at the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) during full-scale traffic testing. The ANN models were trained with results from an axisymmetric finite element pavement structural model. Using the ANN-predicted moduli based on the NDT test results, the relative severity effects of simulated Boeing 777 (B777) and Boeing 747 (B747) aircraft gear trafficking on the structural deterioration of NAPTF flexible pavement test sections were characterized. The results indicate the potential of using lower force amplitude NDT test data for routine airport pavement structural evaluation, as long as they generate sufficient deflections for reliable data acquisition. Therefore, NDT tests that employ force amplitudes at prototypical aircraft loading may not be necessary to evaluate airport pavements.

UAVs in civil airspace: Safety requirements

This addresses topics concerning the development of future Unmanned Aerial Vehicles (UAV) so they can operate safely within the community of the Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO). Studies by the Defense Science Board, the Office of Science and Technology, Government Accountability Office, and the Congressional Research Service Library of Congress have all emphasized that soon there will be a significant number of UAVs operating side-by-side with manned civil aircraft in the FAA's National Airspace System (NAS). It is anticipated that future UAVs will perform many of the dull, dirty, and dangerous civilian missions. In 2006, about 600 UAVs were manufactured in the US alone. Therefore, there is an urgent need for developers of UAVs to understand safety certification for operations in the NAS, and that safety certification starts with safety requirements, safety design, safe development processes, safety verification, and safe operating procedures in the planned operational environment.

Stiffness characterisation of full-scale airfield test pavements using computational intelligence techniques

The falling weight deflectometer (FWD) is a non-destructive test equipment used to assess the structural condition of highway and airfield pavement systems and to determine the moduli of pavement layers. The backcalculated moduli are not only good pavement layer condition indicators but are also necessary inputs for conducting mechanistic based pavement structural analysis. In this study, artificial neural networks (ANNs)-based backcalculation models were employed to rapidly and accurately predict flexible airport pavement layer moduli from realistic FWD deflection basins acquired at the U.S. Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF). The uniformity characteristics of NAPTF flexible pavements were successfully mapped using the ANN predictions.

Simulated aircraft load testing and non-destructive evaluation of bituminous pavements

The US Federal Aviation Administration's National Airport Pavement Test Facility was constructed to generate full-scale accelerated pavement test data for the development of advanced airport pavement design criteria. During the first round of traffic testing, a six-wheel (Boeing 777) landing gear and a four-wheel (Boeing 747) landing gear were trafficked on flexible test pavements until they were deemed failed. Non-destructive tests were conducted at different stages of trafficking to monitor the effect of time and traffic on the structural condition of the pavements. Rut depths were measured at periodic intervals throughout the traffic testing. The primary objective of this study is to characterise the variations in pavement surface deflection under repeated aircraft gear loading and compares the results with the pavement rutting performance trends. The results showed that both the six-wheel and four-wheel test gears produce similar surface deflections and rut depths. There seems to be a correlation between the heavy weight deflectometer surface deflections and rutting performance.

Neural Networks Analysis of Airfield Pavement Heavy Weight Deflectometer Data

The Heavy Weight Deflectometer (HWD) test is one of the most widely used tests for assessing the structural integrity of airport pavements in a non-destructive manner. The elastic moduli of the individual pavement layers predicted from the HWD deflection measurements through inverse engineering analysis are effective indicators of pavement layer condition. The primary objective of this study was to develop a tool for backcalculating non-linear pavement layer moduli from HWD data using Artificial Neural Networks (ANN) for rapid structural evaluation of airfield pavements. A multi- layer, feed-forward backpropagation ANN which uses an error-backpropagation algorithm was trained to approximate the HWD backcalculation function. The synthetic database generated using an axisymmetric pavement finite-element program was used to train the ANN. Using the ANN, the Asphalt Concrete (AC) moduli and subgrade moduli were successfully predicted. Apart from the moduli, an attempt was made to predict the critical pavement structural responses using ANN models. The final product was used in backcalculating pavement layer moduli and predicting subgrade deviator stresses from actual field data acquired at the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF).

PREDICTING CAPACITIES OF RUNWAYS SERVING NEW LARGE AIRCRAFT

This paper presents a simplified approach for predicting the allowable load repetitions of New Large Aircraft (NLA) loading for airfield runways based on Non‐Destructive Test (NDT) data. Full‐scale traffic test results from the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) were used to develop the NDT‐based evaluation methodology. Four flexible test pavement sections with variable (unbound layer) thicknesses were trafficked using six‐wheel and four‐wheel NLA test gears until the test pavements were deemed failed. Non‐destructive tests using a Heavy Weight Deflectometer (HWD) were conducted prior to the initiation of traffic testing to measure the pavement surface deflections. In the past, pavement surface deflections have been successfully used as an indicator of airport pavement life. In this study, the HWD surface deflections and the derived Deflection Basin Parameters (DBPs) were related to functional performance of NAPTF flexible pavements through simple regression analysis. The results demonstrated the usefulness of NDT data for predicting the performance of airport flexible pavements serving the next generation of aircrafts.

The Perceived Need for Training and Potential Training Topics for Indiana Airport Board Members

The Perceived Need for Training and Potential Training Topics for Indiana Airport Board Members

Behaviour of airfield pavement subgrades under load test

The US Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) was constructed to provide full-scale pavement response and performance data under new generation aircraft loading for development and verification of airport pavement design criteria. During the first series of traffic tests, four flexible pavement test sections (two low-strength subgrade and two medium-strength subgrade test sections) were subjected to six-wheel and four-wheel gear loading to assess the relative severity effects. Trench sections were opened at the completion of traffic testing for conducting forensic investigations. In this paper, the effect of full-scale accelerated heavy aircraft gear trafficking on the NAPTF unbound aggregate and fine-grained subgrade layer material properties (referred to as geomaterials) is discussed. The results indicate that the in situ dry densities and moisture contents have decreased in the crushed stone base as a result of trafficking whereas the dry densities of the sub-base (grey quarry blend fines) layer have increased. The low-strength subgrade California Bearing Ratio (CBR) has increased as a result of trafficking, whereas the medium-strength subgrade CBR has decreased. These results can be used to develop input parameters for NAPTF pavement structural modelling and analysis.

Effect of Dynamic Aircraft Gear Loads on Asphalt Concrete Strain Responses

Abstract Asphalt strain gauges were installed in both the longitudinal and transverse directions at the Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) to measure the load-induced Asphalt Concrete (AC) tensile strains during full-scale traffic testing with a dual-tridem Boeing 777 gear configuration and a dual-tandem Boeing 747 gear configuration. The results are presented for four flexible test sections; two sections with 127 mm of AC and two with 254 mm of AC. An axisymmetric finite element pavement analysis software was used to model the NAPTF flexible test sections and compute the AC strain responses. The measured AC strain magnitudes were significantly influenced by AC temperature variations. Dramatic increase in peak strain responses were observed as the NAPTF flexible test sections approached structural failure. There was a good agreement between the field-measured and computed strains during the early life of the test sections.

Pavement moduli variation under heavy aircraft trafficking

Heavyweight deflectometer (HWD) tests at 160·2 kN (36 000 lb) force amplitude were periodically conducted at the US Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) to monitor the effect of Boeing 777 and Boeing 747 test gear trafficking on the structural condition of pavements. In this study, the changes in back-calculated pavement moduli with trafficking were used to compare the relative severity of the aircraft landing gear on the test sections. ILLI-PAVE, an advanced finite-element flexible pavement structural model that can accommodate non-linear unbound material properties was used to model the NAPTF test sections under the HWD loading and synthetic databases were generated. Regression algorithms relating the moduli to HWD deflection basin parameters were developed for predicting asphalt concrete and sub-grade moduli from NAPTF HWD test data. The traffic lane back-calculated moduli values were compared with the untrafficked centreline moduli values to study the loss of stiffness as a result of trafficking. The results were finally compared with those obtained using conventional elastic layer program-based back-calculation software. The results indicate that both test gears have similar potential in terms of their damaging effect on airport flexible pavements.

Applying the common criteria in systems engineering

The National Institute of Standards and Technology has proposed using the common criteria and system-level protection profiles (SLPPs) to specify security requirements in large systems, such as those used in air traffic management. This article summarizes experience with SLPP and security targets for the US Federal Aviation Administration's National Airspace System. The authors review the FAA efforts, highlight the problems encountered, and offer suggestions for future work, calling for more research on linking systems, software, and security requirements engineering with SLPP; clearer ties between security specifications and system certification; and better guidance on the appropriate use of SLPP as a prerequisite to widespread use

Task Analysis of Aircraft Inspection Activities: Methods and Findings

Unless the U.S. commercial aircraft fleet is maintained with high reliability, we cannot be assured of flight safety with an ageing fleet. Maintenance depends upon inspection to be effective, thus the reliability of aircraft inspection is of paramount importance to safety. To provide baseline data on the current inspection activities of commercial aircraft, a task analysis of inspection by commercial carriers was undertaken as part of the Federal Aviation Administration's National Ageing Aircraft Research Program (NAARP). This paper describes the Task Analysis methodology developed, typical results, and some human-system mismatches detected.

The FAA'S Air Traffic Control Simulation Facility

One of the most effective tools for use in air traffic control experimentation, evaluation, and systems studies is the Air Traffic Control Simulation Facility (ATCSF) of the Federal Aviation Administration's National Aviation Facilities Experimental Center located at Atlantic City, New Jersey. The ATCSF combines computer hardware, software, and personnel for testing and evaluating advanced air traffic control concepts and procedures. This paper describes the simulation capability of the ATCSF, its hardware and software, and some of the technical programs supported by the facility.