- ISSUE 4/2008
- Copyright and Credits
- Guest Editorial
- To the Letter
- Winter Operations
- Maintenance and Certification
- Recently Released TSB Reports
- Accident Synopses
- Regulations and You
- Debrief: Flight Crew Awareness of Departure Runway Length
- Self-Paced Study Program
- Full HTML Version
- PDF Version
- Coming Soon to a Theatre Near You: Whiteout
- "Damn, Was That Ever Slippery!"
- A Holdover Time Paradigm Shift
A recent search of Transportation Safety Board of Canada(TSB) statistics for occurrences involving helicopters in a "collision with terrain" accident from 1998 to 2008 yielded 303 hits. Of those 303 accidents, 18 occurred in whiteout conditions. There were 45 passengers on those 18 flights; 23 were injured and 13 lost their lives. The pilot's experience level did not appear to be a factor. In anticipation of the upcoming winter season, and considering the above statistics on the dangerous whiteout phenomenon, we felt it would be worthwhile to reprint the following article, titled "Whiteout," which was originally published in Aviation Safety Vortex 4/2003.
Back in the old days, a Canso was on a very long IFR ferry trip in the Arctic Islands. For the crew it was a monotonous routine-monitoring the instruments and listening to the roar of the two big radial engines just above their heads. There was nothing to see out of the windows, just a white, featureless blank.
It was a boring and undemanding afternoon, until the captain looked out through the windscreen and saw his flight engineer standing in front of the aircraft with a big grin on his face. This came as quite a surprise to the captain, whose training and background had not prepared him for coming face-to-face with anyone while in cruising flight, let alone a member of his crew.
The Canso had flown into very gentle rising snow-covered and featureless terrain. The impact had been so soft and gentle that amidst the rattling, roaring and vibrating that constitutes cruising flight in this type of aircraft, the crew hadn't noticed the deceleration at all. The flight engineer had happened to look out of one of the Perspex blisters in the tail of the aircraft and discovered that he could see the ground, quite motionless just a few feet below him. So he got the aluminum ladder out, climbed down to the ground and walked round to the front to get the pilot's attention.
Maybe it's urban legend; maybe it's a true story-who knows? I suppose, considering the boat-shape of the Canso hull, that it could happen, but one thing's for sure-it's not likely to happen in a helicopter. I do know one chap who claims to have hit the ice at cruise speed in a Bell 206 on fixed floats, and suffered nothing but a gentle bounce, but the more likely scenario involves a catastrophic break-up, and debris field.
Whiteout conditions mean a gradual loss of all visual references
If you are a VFR commercial pilot flying in Canada, sooner or later you are going to experience loss of visual reference to some extent. If you're lucky, it will be for only a second or two before your frantic eyes find a clump of trees or something else that tells you which way is up. If you're not lucky, you'll likely join the ranks of those who have found out the hard way that the "seat of your pants" is easily fooled. For those who haven't experienced it, it can happen something like this:
The weather is deteriorating. You know the situation is not good, but you press on, hoping it will improve. It doesn't-it gets worse, and you find yourself losing good reference. Your eyes are darting from side to side and your pulse increases. You slow the aircraft, still searching for visual clues. Your breathing speeds up, and your pulse is now racing. You feel a cold rush flood through your body, and a strange sensation of your insides relaxing as adrenalin and fear overcome concentration and reasoned thought. Then comes the disbelief; the absolute unwillingness to accept that your body has let you down and you are helpless.
Let's look at some examples of descriptions taken from Canadian accident reports from the past few years:
- During approach for landing on a glacier and at 8000ft above sea level(ASL), the pilot of the 205 entered a whiteout-like condition in swirling snow. He lost all visual reference and touched down hard, causing damage to the skid-gear.
- Nearing destination, the aircraft flew into whiteout conditions. All visual reference was lost before the pilot could complete a landing, and the helicopter rolled over on touchdown.
- The main rotor hit the ground after the left skid dug into snow surface during a mountaintop landing. The aircraft was still in forward motion at touchdown due to wind shift and whiteout.
- The sling load proved heavier than the pilot expected, and he couldn't get airborne. He hovered with the load resting on snow-covered ice and lost visual reference in the blowing snow. The pilot released the sling load, while the helicopter was in a nose-high attitude. The tail rotor struck the snow surface and the machine rolled over.
- The pilot encountered whiteout conditions and attempted to turn back. The aircraft crashed on the Arctic sea ice during the turn.
- The pilot lost visual reference in whiteout over an ice-covered inlet and flew into the ice.
- The pilot aborted his third take-off attempt in blizzard conditions. On touchdown in whiteout conditions, the helicopter rolled on its side.
- The aircraft struck ice in nearly flat attitude in whiteout conditions...
- The 206 pilot took off on a charter with two passengers for some survey work. The weather was marginal but there were no weather reporting stations in the area, so they decided to "have a look at it." When they turned out over the sea ice to look for some fuel barrels, the pilot soon found himself in whiteout. He asked a passenger to keep an eye on the altitude while he turned the 206 to regain visual reference with the shoreline. In the turn he lost altitude and the helicopter struck the ice.
This accident resulted in three serious injuries. One has to wonder about what was going through the pilot's mind when he asked the passenger to "keep an eye on the altitude." -Ed.
- The ceiling was low and the visibility was poor, in falling snow, but the 206 pilot spotted his party on the lake. Day-Glo cloth markers indicated their location. The ice was covered with four inches of fresh loose snow. As the helicopter entered a pre-landing hover, the rotor wash blew up the loose snow and the pilot became disoriented. The machine rolled and the main rotor blades struck the ice.
- The 206 was number two in a group of six helicopters en route from Charlottetown, P.E.I., to an ice flow in the Gulf of St. Lawrence to observe the seal-hunting operation. As the group approached the halfway point, they encountered whiteout conditions in light-to-moderate snow. The ice they were flying over was relatively flat and also featureless. The accident helicopter reduced speed to about 60 kt and descended in an attempt to maintain visual contact with the ice. As the helicopter neared the ice, number-three aircraft radioed a warning to pull up, but the warning came too late. The 206 hit the ice with sufficient force to tear the float gear off and crush the crew and passenger seats.
- The pilot landed in a mountain meadow to pick up skiers. As the helicopter did not come out of the whiteout as expected on takeoff, the pilot aborted. The right skid dug in and the machine rolled over.
Sadly, there are many more examples; they happen every year. What may surprise you is that many of them happen in the summer months, when Mother Nature hasn't yet released her grip on winter in our northern regions. One study found that in the preceding nineyears,25percent of the whiteout accidents took place during the summer operational season. This may indicate that currency plays a role in both the hands-on skills and decision making required to deal with winter weather.
The vast majority of low-speed take-off and landing accidents are preventable by good decision making, with careful consideration given to:
- the conditions of the area;
- the recent weather, wind, temperature(is the snow heavy, or light and fluffy?);
- patience; and
- technique(see "Snow Landing and Take-off Techniques" in Aviation Safety Vortex 1/2003).
In the en route phase of flight, many human factors gurus and experienced pilots theorize that the stage is set for the accident long before the whiteout condition exists. They believe that if you start the trip with the mindset that you'll return or divert if the weather deteriorates beyond a given point, you are more likely to do so when it does. Conversely, if you have nothing but the destination or an optimistic forecast in mind, you're more likely to press on. This is definitely something to consider when planning your next flight into the frozen Canadian winter.
Runway excursion due to slippery runway
There isn't a pilot in Canada operating high-performance aeroplanes who hasn't uttered or heard someone utter something akin to the title of this article.
Operations on contaminated runways raise numerous questions from air operators. However, air operators aren't the only ones operating under cold or inclement weather conditions interested in gaining a better understanding of the factors that influence aeroplane braking performance on non-bare and -dry runways. Their flight crews want to know more, too. While air operators are justifiably more concerned with minimizing the payload loss and maximizing their revenue, flight crews are more interested in maintaining a high level of safety in their own operation.
Hence, this article is directed at flight crews who want to know more about the why of contaminated runway operations than the what. The what, they are taught in the many ground school sessions they attend on the subject, generally at the expense of the why.
It doesn't take a rocket scientist to figure out that a slippery runway affects the braking performance of an aeroplane. Any time you find yourself in a snowstorm, driving on one of Canada's highways, you will automatically slow down, impelled by a strong sense of survival, because you instinctively know that it will take you a longer distance to stop. Guess what? The same is true for an aeroplane. In fact, even more so, because as all flight crews know, aeroplanes tend to make poor road vehicles! There are, of course, other issues that flight crews must consider when operating an aeroplane on a contaminated runway, such as loss in acceleration performance, if the contamination is deep enough on takeoff, say, or loss in aeroplane lateral controllability on a contaminated runway that just happens to be slippery and in a crosswind condition at the same time.
This article will not address all the aspects of operating an aeroplane on a contaminated runway. Instead, for the most part, the article will focus on the following:(1) what the measurement provided by a runway-friction measuring device means;(2) the difference between some of these devices; and(3) the difference between what these devices measure, that is, the difference between what is called a runway friction coefficient-or runway friction index or coefficient of runway friction-and the braking coefficient-or weight on wheels coefficient-experienced by an aeroplane. The runway friction coefficient and the braking coefficient are NOT the same thing, and this difference has lead to much confusion for flight crews because the manufacturers produce data using braking coefficient, while the airport operators report runway friction coefficient.
There shouldn't be any conflict between operating an aeroplane safely and being economically viable in the process. In fact, it just makes good economic sense to operate safely at all times, while recognizing that to do so in adverse conditions may have an economic penalty. Pay it, and move on, or don't operate!
Canadian Runway Friction Index(CRFI)- Application to Aircraft Performance
The information provided below, including information on the CRFI tables,(which have not been provided in this article due to space requirements) is drawn from the Aeronautical Information Manual (TC AIM) and can be found at the following Web site: http://www.tc.gc.ca/eng/civilaviation/publications/tp14371-air-1-0-462.htm#1-6.
The data compiled in Table 1 (CRFI Recommended Landing Distances[No Discing/Reverse Thrust]) and Table 2 (CRFI Recommended Landing Distances[Discing/Reverse Thrust]) is considered to be the best available at this time because it is based upon extensive field-test performance data of aeroplane braking on winter-contaminated surfaces. Pilots will find the data useful when estimating aeroplane performance under adverse runway conditions. The aeroplane manufacturer is responsible for producing information and providing guidance or advice on the operation of aeroplanes on a wet and/or contaminated runway. The information below does not change, create any additional, authorize changes to, or permit deviations from other, regulatory requirements. The tables are intended to be used at the pilot's discretion. Regulations and associated standards have been drafted on the use of the CRFI tables, and they are currently undergoing regulatory review.
Because of the many variables associated with computing accelerate-stop distances and balanced field lengths, it has not been possible to reduce the available data in such a way as to provide CRFI corrections applicable to all types of operations. Consequently, pending further study of the take-off problem, only corrections for landing distances and crosswinds are included.
It should be noted that in all cases the tables are based on corrections to flight manual dry-runway data and that the certification criteria does not allow consideration of the extra decelerating forces provided by reverse thrust or propeller reversing. On dry runways, thrust reversers provide only a small portion of the total decelerating forces when compared to wheel braking. However, as wheel braking becomes less effective, the portion of the stopping distance attributable to thrust reversing becomes greater. For this reason, if reversing is employed when a low CRFI is reported, a comparison of the actual stopping distance with that shown in Table 1 will make the estimates appear overly conservative. Nevertheless, there are circumstances, such as crosswind conditions, engine-out situations and reverser malfunctions, that may preclude the use of thrust reversing.
The landing distances recommended in Table 1 are intended to be used for aeroplanes with no discing and/or reverse-thrust capability and are based on statistical variations measured during actual flight tests.
Notwithstanding the above comments on the use of discing and/or reverse thrust, Table2 may be used for aeroplanes with discing and/or reverse-thrust capability and is based on the recommended landing distances in Table 1, with additional calculations that give credit for discing and/or reverse thrust. In the calculation of distances in Table 2, the air distance from the screen height of 50 ft to touchdown and the delay distance from touchdown to the application of full braking remain unchanged from Table 1. The effects of discing and/or reverse thrust were used only to reduce the stopping distance from the application of full braking to a complete stop.
The recommended landing distances stated in Table 2 take into account the reduction in landing distances obtained with discing and/or reverse-thrust capability for a turboprop-powered aeroplane and with reverse thrust for a turbojet-powered aeroplane. Representative low values of discing and/or reverse-thrust effect have been assumed; therefore, the data may be conservative for properly executed landings by some aeroplanes with highly effective discing and/or thrust-reversing systems.
The crosswind limits for CRFI given in Table 3 contain a slightly different display range of runway-friction index values from those listed in Table 1 and Table 2. However, the CRFI values used for Table 3 are exactly the same as those used for Table 1 and Table 2 and are appropriate for the index value increments indicated. Further, it should be noted that the crosswind limits listed in Table 3 are not based on actual flight-test results, as are Table 1 and Table 2, because the hazards associated with such actual testing conditions were considered to be too great. To the best knowledge available, the results contained in Table 3 are based on a best estimate and have been available to flight crews in this very same format for many years.
Table 4 has also been updated based on the best data available, which was generated as a result of the testing program that helped produce Table 1 and Table 2.
Some additional comments about Table 1 and Table 2 are appropriate here.
Hidden in the tables is a middle step used in the development of the quoted distances. The first step was the correlation of the friction-measuring device used in Canada to measure runway friction, namely, a spot-measuring electronic decelerometer, to the μ(pronounced mu) braking coefficient of several aeroplanes that were tested during the winter runway contamination project. In order to develop landing distances in terms of the μ braking coefficient of any aeroplane, once certain values are assumed for the μ, all that is required is Newton's Second Law-just some physics. The decelerating force is a function of the assumed aeroplane braking coefficientμ. Hence, once the correlation had been established between the measured runway-friction values and the braking coefficient of the tested aeroplane μ, the measured runway-friction values were used to calculate the stopping distances instead of some assumed aeroplane braking coefficient. Some manufacturers have stated positions indicating that it is not possible to take a runway-friction measuring device and correlate it well enough to the μbraking of an aeroplane. Based on extensive testing on winter surfaces in Canada and elsewhere, correlation coefficients over 90percent have been consistently obtained for a wide range of aeroplane types. It's time for minds to change!
The methodology used to derive CRFI tables is described in a number of reports published by the National Research Council of Canada(NRC). The methodology has also been adopted by a US-based standards organization: ASTM International. To a line driver, the preceding is just meaningless information. This information is provided only because there is a lot of technical literature available to those who want to dig for it. For example, during the production of CRFI, the researchers involved knew they were making a lot of errors-not mistakes of omission, but what we call known errors. These are errors that the researchers could do nothing about during the measurement process, but that had to be accounted for somehow. Using their best engineering judgment, the researchers decided to estimate what errors were being made and account for those errors in the final product you see as the CRFI tables. The generated data was heavily skewed to the lower friction numbers because that's where the highest risks of operating aeroplanes on winter surfaces are found. When all the errors were added up, an accuracy level of close to 95percent was achieved, which is why the tables come with the reported 95percent level of confidence attached to them. In statistical analysis, this has a name. And for your next beer call, when you want to really impress, it is called a non-parametric statistical approach. Subsequent to this, statistical analysis was applied to the skewed data, what is called re-normalizing the so-called non-normal data to make it normal-nothing more than the familiar bell curve you used to get in university and college. It turned out that the data we had collected came in at over a 99percent level of confidence. That's the long way of saying that it's pretty damn good data! Still, to account for the known errors being made, there is about 1 000ft of error added in at the lower CRFI numbers and about 700ft at the higher numbers to account for numerous factors, such as variation in friction cart readings across vehicles, friction levels changing on the runway, etc. This is all described in the early NRC reports referred to above.
How should the CRFI tables be used? This is a business decision that has to be made by every user. Linear interpolation within the tables is O.K., but it's best to simply go to the next most conservative value. The tables are entered from the top with the CRFI value and from either the left- or right-hand columns with either landing distance or landing field length, as appropriate. For example, for a CRFI value of 0.32 and a dry landing distance of 2 500ft, use 0.30 and 2 600 ft to avoid the interpolation. Extrapolation outside the tables is not recommended.
More needs to be said about the difference between landing distance and landing field length, the so-called 60percent and 70percent dispatch factors. There are many issues about aeroplane certification performance that today's flight crews do not understand and that are simply not being addressed in any training material available to them or in a way that is understandable in terms of "pilotees." One issue that is consistently misunderstood is the difference between landing distance and landing field length, which is described below.
There are operational dispatch factors that provide required landing field length and that are derived from landing distance. Note that dispatch factors or landing field length is an operational requirement, NOT a certification requirement, although some manufacturers include landing field length data or charts in the performance sections of their aircraft flight manuals(AFM), as noted earlier. Once the aeroplane is airborne, the dispatch factors no longer apply; only landing distance applies. For turbojet aeroplanes, the dry dispatch factor is calculated by multiplying the landing distance by 1/0.6=1.67. For turboprop aeroplanes, the dry dispatch factor is calculated by multiplying the landing distance by 1/0.7=1.43. As convoluted as the preceding appears, it is reproduced here because that is the way you will see it expressed in operational regulations. Most regulations on this subject, regardless of the authority that produces them, are almost incomprehensible. It is simply best to think of the numbers 1.67 and 1.43, as applicable, times the dry landing distance to obtain the dry landing field length. Clear!
How do you deal with an unserviceable component, for example, a zero flap landing? If it becomes necessary to apply corrections to the dry landing distance, simply enter the appropriate CRFI table with the normal, serviceable landing or field-length distance, as appropriate, to determine the recommended landing distance, assuming no unserviceable component existed. Then apply any additional corrections specified in the AFM for any aeroplane unserviceable component to the distance just obtained from the CRFI tables; otherwise, you will find yourself trying to use the CRFI tables outside the bounds. Again, extrapolation outside the tables is not recommended. The CRFI tables assume the anti-skid system is functioning normally.
Some concerns have been raised regarding the contaminated surfaces on which the testing was conducted to develop CRFI, the implication being that the results used to obtain CRFI are only applicable to those types of surfaces. The testing to obtain CRFI was conducted on mostly compacted snow and ice. These surfaces were used to obtain the desired low-friction numbers. Which other surfaces were we supposed to test on? CRFI is a non-dimensional number. It has no units and, hence, is not a function of the surface. If you get a decelerometer reading on some surface of, say, 0.2, then the CRFI tables would be applicable.
The presence of contaminants on a runway affects the performance of any aeroplane by(1) reducing the friction forces between the tire and the runway surface,(2) creating additional drag due to the contaminant impingement spray and displacement drag, and(3) leading to the potential for hydroplaning to occur.
There is a fairly clear distinction between the effect of soft contaminants and hard contaminants. The hard contaminants, like compacted snow and ice, reduce the friction forces only, while the soft contaminants, such as water, slush and loose snow, not only reduce the friction forces, but also have the potential to create additional drag and may lead to hydroplaning.
To develop a model of the reduced braking according to the type of contaminant is a difficult task, to be sure. That said, there is a runway-friction measuring device being used in Canada that has been successfully correlated to the braking coefficient of several aeroplanes, so that at least under certain contaminated runway conditions, such as compacted snow and ice, braking coefficient on a contaminated surface no longer has to be derived from some theoretical values on a dry runway-a highly suspect procedure at best. There appears to be no better substitute for actually measuring the value of friction on the runway and correlating that value to the braking coefficient of an aeroplane.
This article explores a paradigm shift in the operational use of Holdover Time(HOT) information. A brief history of the origins and use of HOT will be presented. This will be followed by a historical account of the industry and authority efforts to bring about a paradigm shift to the operational use of HOT information. The potential benefits and opportunities provided by using such a system will be highlighted.
This article was made possible through the collaboration and contribution of the following individuals: Peter Graverson of D-ICE, Mike Chaput of APS Aviation, Mark Homulos of WestJet, and Bill Maynard of Transport Canada.
The operation of aircraft during ground-icing conditions poses potential safety of flight hazards that must be addressed. Contamination consisting of frost, ice, snow, and other frozen particulate create flight hazards. These contaminates must be removed prior to takeoff(Canadian Aviation Regulation[CAR]602.11). Between 1969 and 2007, ground-icing-related accidents have contributed to over 500 deaths and significant property loss.
The threat is very real! Some of you will remember the Dryden accident. For those who don't, the March10,1989, accident of a FokkerF28-1000 claimed the lives of 24people(see photo, above). As a result of that accident, a commission of inquiry, led by The Honourable Virgil P.Moshansky, was instituted. Public hearings lasted 20 months and 166individuals were interviewed. Thousands of pages of transcripts and evidence were condensed into a four-volume report. Typical of many accidents, there were a number of causal factors. One of the principle causal factors was attempting to take off with contamination on the aircraft's critical surfaces. The report concluded with 191 recommendations in 19distinct areas. The publication of the report led to extensive regulatory changes. Furthermore, a deluge of research and development(R&D) activities were initiated. These R&D activities brought scientific support to clarify acceptable processes and procedures associated with wintertime operating conditions. Time and space preclude the discussion in this article of R&D conducted by Transport Canada in these areas over the past 20years. Interested readers can view and download many of the R&D reports by visiting the following Web site: Transportation Development Centre.
There are a number of methods that can be used to remove frozen contaminates from the aircraft surfaces prior to takeoff. The most widely-used method for large aircraft is the use of de-/anti-icing fluids. The focus of this article is on the evolution of HOTs and their operational use.
Figure1: Early HOT table(circa 1989)
As a result of the significant work conducted by the SAEG-12, eventually aerospace standards and recommended practices were developed and published, defining fluid properties, testing methods, acceptable application procedures, etc. By the late 1990s, some of this work led to a standardization of the HOT Guidelines, domestically and internationally, see Figure2: Recent HOT table(2007). Transport Canada and the U.S. Federal Aviation Administration(FAA) publish HOT Guidelines for operational use on an annual basis(www.tc.gc.ca/eng/civilaviation/standards/commerce-holdovertime-menu-1877.htm). The HOT Guidelines formats are by their nature limited in terms of the information they can provide to the flight crew.
The information has been simplified to ensure its ease of use, especially during the busy ground-operational phase. HOT Guidelines provide the flight crew with HOTs for a range of precipitation types, precipitation rates and temperature bands.
Establishing HOT Guidelines
Every year, the FAA and Transport Canada, on behalf of fluid manufacturers, assess the HOT performance of fluids in both laboratory and natural conditions on a cost-recovery basis.
In the laboratory, the tests are conducted under defined and controlled conditions of precipitation type, precipitation rate, and temperature.
Rectangular aluminium plates, coated with the de-/anti-icing fluid being tested are exposed to various types of precipitation.
The quantity of precipitation, also known as liquid water equivalent(LWE), is measured using pans. LWE is measured in units of grams/decimeter squared/hour.
Specific failure criteria are used to identify when the fluid on the test plates is considered failed. The amount of LWE required to reach the failure point is then documented and graphed as a data point. This allows the creation of regression curves and associated regression coefficients. These curves plot fluid failure time on the vertical axis versus precipitation rate on the horizontal axis. This information is then assessed and converted into the HOT Guidelines that many flight crew are familiar with.
Unfortunately, the existing HOT Guidelines assume that the pilot has accurate, real-world information on which to base their decision making.
What information is actually available to the pilot when using the HOT Guidelines? Remember that one needs accurate temperature, precipitation type and precipitation rate to use the HOT Guidelines effectively.
Temperature is almost always available, either through ATC or meteorological reports, or by direct cockpit reading.
Although precipitation type is available through aviation routine weather reports(METAR), there are cases where this information is not updated frequently enough for ground de-/anti-icing operations.
The precipitation rate reported in METARs(as light, moderate, or heavy) is not correlated with LWE used during fluid testing. The result is that the pilots must make a subjective assessment, integrating the various parameters and then consulting the HOT Guidelines. It is plausible that different pilots could draw different conclusions from the same reported or observed weather conditions.
To recap, the HOT Guidelines are generated using a scientific approach to ensure their accuracy and consistency. The operational use of the guidelines is based largely on a subjective assessment of the weather conditions. This is due in large part to the fact that the current weather reporting and observing infrastructure was not designed for use with de-/anti-icing activities.
Is there a better way of making use of all this scientific HOT data?
Holdover Time Determination Systems(HOTDS)
In 2003, Transport Canada was approached by DAN-ICE, now called D-ICE. D-ICE is a Danish company developing meteorological and support equipment for use with HOTs. At that time, they were requesting approval or certification of a system that would simplify the way flight crews obtained their HOTs.
Largely as a result of that original request, Transport Canada supported industry initiatives that would improve the way HOT information is provided and used by pilots and operators in making safety-critical decisions, thus directly promoting safety and aeronautics in Canada.
Transport Canada, as the regulatory authority involved with wintertime aircraft operations and associated R&D, was poised to promote new systems that assist pilots and operators in better coping with wintertime operations. The system can also be thought of as an automated electronic version of the HOT Guidelines. The term Holdover Time Determination System(HOTDS) was coined to describe this system, and will be used throughout the remainder of this article.
D-ICE HOTDS equipment
The HOTDS uses the regression curves and coefficients generated during the fluid endurance testing previously described in this article. The regression coefficients are published in a Transport Canada report. The current report only contains coefficients for the two fluids used at sites where the HOTDS is currently installed.
This was the first time such a system would be implemented anywhere in the world, and therefore, a shift in cultural and operational thinking was required. To begin with, there were no standards or design requirements associated with this type of system. Furthermore, the availability of LWE information for ground de-/anti-icing operations through regular meteorological channels was, and currently still is, unavailable.
Transport Canada contracted APS Aviation to conduct R&D into the development of a performance-based standard that would initially be included as part of a regulatory exemption(similar to the automated weather observation system[AWOS]exemption). Eventually, the performance-based standard could be incorporated within the CARs as a regulatory standard. The development of the performance-based standard took twoyears. Simultaneously with the development of a performance-based standard, Transport Canada was formulating the necessary exemption criteria to support operational implementation of the HOTDS.
WestJet had shown a keen interest in the potential for using the HOTDS. WestJet and D-ICE paired up to conduct initial operational suitability trials during winter 2005–2006 and 2006–2007.
Operational use of the HOTDS was kept as simple as possible. The flight crew would initiate a request for a HOT via the Aircraft Communications Addressing and Reporting System(ACARS). The latest information from the HOTDS, which provides updates every 10 min, would be sent back to the flight crew through the ACARS as a single HOT value for the current weather conditions. The HOT information would then be displayed on the flight deck flight management system(FMS).
Potential benefits associated with the HOTDS included:
- providing pilots with better HOT information on which they could base their decisions;
- providing pilots with the most appropriate HOTs, thus minimizing confusion and errors during the extremely busy ground-operational phase;
- the ability to select the most appropriate fluid type for the given conditions, thereby minimizing environmental impact;
- a potential cost savings associated with optimum fluid selection.
In December2007, Transport Canada issued a one-off regulatory exemption to WestJet, allowing them to use a HOTDS in place of paper HOT Guidelines at a limited number of airports. It is expected that full operational use of this system will be in place for the 2008–2009 winter season.
Use of the system is contingent on the operator:
- revising their company operations manual;
- conducting the appropriate training;
- having contingency plans;
- ensuring the HOTDS equipment is declared as meeting the performance-based criteria; and
- having the appropriate HOTDS equipment in place at selected airports.
The use of the exemption approach allows limited operational usage of HOTDS, since the onus is on the air operator to ensure that the HOTDS is installed and declared compliant. To truly reap the full benefits of HOTDS, it is necessary to ensure that the requisite meteorological information for de-/anti-icing purposes is disseminated through regular meteorological channels.
In order to obtain maximum benefits to aviation for improved decision-making capabilities regarding anti-icing and de-icing decision making, it is important that a common global approach be taken, to the extent practicable. Transport Canada is working within the International Civil Aviation Organization(ICAO) and the World Meteorological Organization(WMO) to develop common methods for assessing and communicating information in support of operations under icing conditions. At present, efforts are focusing on whether this data should be added to METARs or aviation selected special weather reports(SPECI) at select stations, and the FAA already has plans to do so for some aerodromes in the not-too-distant future.
2008–2009 Ground Icing Operations Update
In July2008, the Winter2008–2009 Holdover Time(HOT) Guidelines were published by Transport Canada. As per previous years, TP14052, Guidelines for Aircraft Ground Icing Operations, should be used in conjunction with the HOT Guidelines. Both documents are available for download at the following Transport Canada Web site: www.tc.gc.ca/eng/civilaviation/standards/commerce-holdovertime-menu-1877.htm. If you have any questions or comments regarding the above, please contact Doug Ingold at email@example.com.
Flight Crew Survey on Takeoffs in Freezing Drizzle or Freezing Rain
Transport Canada(TC) has initiated a Working Group to better understand the current operational practice of taking off during freezing rain or freezing drizzle conditions. To this effect, an independent third party will be administering a survey on TC's behalf.
As a pilot, your participation in this survey will assist TC in determining whether additional guidance material, further interpretation of regulations and standards, or additional regulations and standards are required in the area of takeoff in these conditions. TC is also taking this opportunity to collect information related to takeoff during conditions of ice pellets.
The survey is targeted predominately to IFR-rated pilots who operate in winter conditions. We encourage these pilots to complete the survey, which can be found at the following Web address: http://snaponline.snapsurveys.com/surveylogin.asp?k=121576066574.
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