- ISSUE 1/2011
- Copyright and Credits
- Guest Editorial
- Air Taxi Floatplane Operations Workshop Brings B.C. Operators Together
- Flight Operations
- Maintenance and Certification
- Recently Released TSB Reports
- Accident Synopses
- Regulations and You
- Debrief: From the FAA: Loose Equipment in the Flight Compartment and on Glare Shields
- National Aviation Day (poster)
- Take Five: NOTAMs
- Full HTML Version
- PDF Version
- Unauthorized Low Flight Claims Flying Instructor and Student
- Fuel Gauges: Do they Indicate Properly?
- CFIT: Why Are Aircraft Flying at Minimum IFR Altitudes?
The following is a condensed version of Transportation Safety Board of Canada (TSB) Final Report A09Q0065 on the fatal wire strike and crash of a Cessna 150L near Saint-Louis, Que. Readers are encouraged to read the full report on-line at www.tsb.gc.ca.
On May 4, 2009, a Cessna 150L with an instructor and a student onboard departed Montréal/Saint-Hubert Airport, Que., on a training flight. The aircraft was flying in a north-easterly direction at low altitude over the Yamaska River, Que., when it collided with a telephone cable spanning the river from west to east. The aircraft impacted the surface of the water and sank. The instructor was fatally injured, while the student pilot was able to exit the aircraft but subsequently drowned. The occurrence took place at approximately 16:37 Eastern Daylight Time (EDT).
The ab-initio student pilot had started training only a week earlier and had no previous flying experience. In those seven days, the student pilot received three hours of ground instruction, spent 1.6 hours in a simulator, and had 1.8 hours of flying time. The occurrence flight was the student pilot’s third planned flight, which was preceded by the relevant ground instruction and pre-flight briefing. This lesson was to cover straight and level flight, climbs and descent exercises as described in the flight training unit’s (FTU) training program. Weather conditions were ideal and not considered a factor.
The instructor made a position report once they reached the training area to the north; however, no other radio calls were made. The last valid radar position at 16:33 EDT shows the aircraft at an altitude of 1 340 ft above sea level (ASL) on a true track of 341° with a ground speed of 90 kt. The last coasting target of the aircraft was captured at 16:34 EDT. The radar floor is approximately 1 000 ft ASL in the area of the occurrence. After 16:34 DT, while flying below the radar floor, the aircraft flew at low altitude at approximately 200 ft above ground level (AGL) towards the village of Saint-Louis, heading in a north-westerly direction. The aircraft then headed northeast at low altitude, descending below 100 ft AGL over the Yamaska River. Hundreds of geese on the riverbank took flight as the aircraft passed by at low altitude. While heading northeast in level flight, at tree-top height, and over the river, the aircraft travelled a total distance of approximately 2.4 km before colliding with the unmarked telephone cable. The aircraft struck the cable with a 30° bank angle and then struck the surface of the water in a nose-down attitude and sank quickly.
Wreckage and impact information
The cable consists of a telephone cable covered with black protective sheathing lashed to a steel cable (see Photo 1). The cable did not break on impact.
Photo 1: Cable specimen from occurrence site
Examination of the aircraft determined that the propeller was being driven by the engine when the cowlings departed the aircraft and continuity of the flight controls was confirmed. Impact marks and material transfer from the telephone cable were noted on the engine crankcase vent line. The impact marks on the vent line had the same spacing and width as the wires of the steel cable that support the telephone cable (see Photo 2).
Photo 2: Cable markings on crankcase vent tube
Examination of the exhaust stacks, the oil pressure gauge, and the electrically powered turn coordinator further confirmed that the engine was developing power when it struck the telephone cable and electrical power was available. The aircraft was found to be maintained in accordance with the regulations, and the weight and centre of gravity were within prescribed limits.
The training flight was conducted in uncontrolled Class G airspace up to 2 200 ft ASL and where air traffic control (ATC) has no authority or responsibility to control air traffic. The training area is situated over mainly small wooded areas, farm fields, and small towns. Had the flight instructor been managing an emergency requiring a precautionary or an emergency landing, the many surrounding fields available would have been suitable. Examination of the aircraft did not identify any anomalies that would have forced the flight instructor to execute a precautionary or emergency landing, and no emergency radio call was made.
The telephone cable spans the Yamaska River west to east and provides telephone service for residents located on either side of the river. It was installed unmarked in 1975 under the grounds that the cable was not deemed a hazard to small craft navigating the river. The Canadian Aviation Regulation (CAR) 621.19–Standards Obstruction Markings specifies that an obstruction should be marked or lighted if its height and/or location are deemed to be a threat to aviation safety. As the telephone cable height was approximately 52 ft (16 m) ASL, it would not be deemed a hazard to aviation. Furthermore, the cable is not in proximity to an airport, aerodrome, or water aerodrome.
The unmarked black cable spans from two 40-ft-high telephone poles located on either side of the 300-ft-wide river. Because of the limitations of the human eye, it is difficult to perceive a wire or cable if the background landscape does not provide sufficient contrast. The fact that the cable was not marked likely made it difficult to detect. Pilots are usually taught to look for telephone poles or towers in order to identify the presence of cables or wires. The telephone poles located further inland from the shoreline were not visible while heading northeast along the river; they were hidden amongst brush and tall trees.
Flight training unit
As for all FTUs in Canada, the unit’s operations are overseen by Transport Canada. It conducted audits in 2005 and again in 2008; this reflects a normal audit scheduling frequency. The 2008 audit concluded that the operator was able to conduct business safely and professionally while conforming to the regulatory requirements.
The flight instructor was certified and qualified in accordance with existing regulations to conduct the training flight, and he was regarded as a capable, responsible, and professional employee. The investigation into this occurrence did not reveal any previous deviations from planned flight exercises or regulations.
Click on image to enlarge.
Several provisions within the CARs apply to low altitude flight:
No person shall operate an aircraft in such a reckless or negligent manner as to endanger or be likely to endanger the life or property of any person. [CAR 602.01]
Because the flight took place over a non-built-up area, Except where conducting a take-off, approach or landing or where permitted under section 602.15, no person shall operate an aircraft (...) at a distance less than 500 feet from any person, vessel, vehicle or structure. [CAR 602.14(2)(b)]
A person may operate an aircraft, to the extent necessary for the purpose of the operation in which the aircraft is engaged, (...) where the aircraft is operated without creating a hazard to persons or property on the surface and the aircraft is operated for the purpose of (...) flight training conducted by or under the supervision of a qualified flight instructor. [CAR 602.15(2)(b)(iv)]
The FTU’s operations manual states that visual flight rules (VFR) dual-instruction flight manoeuvres should not be conducted below 500 ft AGL except for the purpose of takeoff, landing, or forced landing. The objectives of the lesson did not require flight below 500 ft AGL. It is not known why the instructor deviated from the training exercise and known regulations, and conducted the last portion of the flight at low altitude over the river.
The Flight Instructor Guide covers the subject of flight safety and stresses the need for the instructor to always use correct safety practices because he or she is a role model to others.
Given the student pilot’s limited aviation knowledge and flying experience, it is assumed that the flight instructor was at the controls at the time the aircraft travelled at low level over the river and collided with the telephone cable.
Because there were no survivors, the reason the instructor deviated from the training exercise and conducted the last portion of the flight at low altitude over the river is unknown. Flight at low altitude was not required for the exercises to be taught nor was it accepted practice as per the CARs or company procedures.
Cables may be unmarked if they are determined to be neither an aeronautical nor a navigable waters hazard. The telephone cable spanning the Yamaska River was not considered a hazard to aviation in that it was approximately 52 ft ASL, at the approximate height of the river banks and was not in the vicinity of an airport, aerodrome, or water aerodrome. The fact that the cable was unmarked made it more difficult to detect. Furthermore, the telephone poles on either side of the river, a primary indicator of the presence of a cable, were hidden by trees and brush. Low flying increases the risk of collision with cables and other structures.
Aircraft electric power, engine power, and flight control continuity were confirmed for the time at which the aircraft collided with the telephone cable; therefore, it is unlikely that the flight instructor was managing an emergency, which would justify low level flight over the river. There were many fields in the area, which would have been suitable had the flight instructor needed to execute an emergency or precautionary landing; the river would not have been a primary choice. The absence of any communication advising of an emergency situation reduces the likelihood that such a situation existed.
Findings as to causes and contributing factors
The aircraft was flown at low altitude, causing it to collide with an unmarked telephone cable suspended 60 ft ASL over the Yamaska River.
Flying below 500 ft AGL was not required, given the planned exercises to be demonstrated during the training flight; the reason for deviating from the lesson plan and the school’s procedures is unknown.
Finding as to risk
- Low flying poses additional risks to pilots. Cables and other obstacles may be unmarked if they are determined to be neither an aeronautical nor a navigable waters hazard. Unmarked cables are difficult to detect.
Safety action taken
Although not required by regulation, but in light of recently reported low flying over the river since the occurrence, the telephone company has installed red and white markers on the telephone cable spanning the Yamaska River.
by Tom Bennett, Civil Aviation Safety Inspector, Aircraft Maintenance and Manufacturing, Prairie and Northern Region, Civil Aviation, Transport Canada
There have been multiple incidents of fuel exhaustion over the past few years. In the last issue of the Aviation Safety Letter (ASL), you read about fuel starvation due to improper fuel selector condition. In this article, I would like to talk about another common factor in fuel starvation incidents: fuel gauges that do not indicate properly.
Some incidents were very public, whereas most incidents went unnoticed with the exception of being listed in the Civil Aviation Daily Occurrence Reporting System (CADORS). Some incidents were directly related to poor fuel management by the flight crew(s); however a few came as a surprise to the flight crew, as the fuel gauge(s) still indicated there was fuel in the tanks. An accurate reading of the fuel gauge may have prevented many of these occurrences.
There is some confusion about the need for serviceable fuel gauges. This confusion is especially prominent in the general aviation world. As both an aircraft maintenance and manufacturing inspector and an enforcement investigator, I have heard statements like: “The gauges have never worked properly. I just keep track of time in my tanks,” many times.
Such a statement is contrary to Canadian Aviation Regulation (CAR) 605.14(j)(i), which states: “No person shall conduct a take-off in a power-driven aircraft for the purpose of a day VFR flight unless it is equipped with a means for the flight crew, when seated at the flight controls to determine the fuel quantity in each main fuel tank […]”. This regulation is then carried through in sections 605.14, 605.15, 605.16 and 605.18 of the CARs, to apply to all power-driven aircraft in all nature of flights (day/night visual flight rules [VFR]/instrument flight rules [IFR]).
Furthermore, many aircraft must have their fuel gauges working as per their type certificates. For larger aircraft, especially transport category aircraft, the fuel gauges can be deferred by means of the minimum equipment list; however, this usually involves using other measuring devices installed on the aircraft and making complex calculations.
A common factor in fuel starvation incidents:
fuel gauges that do not indicate properly
Recently, a commercial pilot was fined because one of his fuel gauges was not working while he was operating an aircraft. In this case, as in others, the fuel exhaustion caused substantial damage to the aircraft during the forced landing. The pilot applied to the Transportation Appeal Tribunal of Canada (TATC) to seek relief from the $750. The TATC upheld the Minister’s decision.
The Aviation Enforcement Branch has also sanctioned aircraft owners and operators for unserviceable fuel gauges found during Transport Canada’s oversight activities. The maximum sanctions for an infraction under CAR 605.14, 605.15, and 605.16 are $3,000 for an individual and $15,000 for a corporation. The maximum sanctions for an infraction under CAR 605.18 (IFR) is $5,000 for an individual and $25,000 for a corporation. Inspection, maintenance and repair of a fuel indication system seem less costly, in my opinion.
Another common excuse I hear is that the gauges have always displayed faulty readings or they are too difficult or expensive to calibrate. As an aircraft owner, if you rely on this flawed thinking you are exposing yourself to numerous risks. First and foremost, you risk running out of fuel. This can lead to personal injury/fatality and damage/loss to the aircraft. Second, you are exposed to regulatory action by enforcement (fine or suspension). I think we can all agree that none of these are pleasant outcomes.
For the aircraft maintenance engineers (AME) in this scenario, I have not yet seen an inspection where the functionality of the fuel quantity indication system is not checked. Be careful what you sign for on the inspection forms and subsequently, the maintenance release. Following manufacturers’ instructions for inspection, maintenance and repairs will never lead you astray.
Most pilots and AMEs are aware that any accident or incident results from a series of events; there is never just one cause. Anything we can to do tighten up against the possibility of an error is a step in the right direction.
Reminder to Always Do a Thorough Preflight Visual Inspection
From time to time, we get excellent photos that need little commentary. Thank you to Neil Ayers and Dan Ferguson, from Northern Ontario, who provided these undisputable proofs that a thorough preflight visual inspection will save the day.
More than a decade after the publication of Controlled Flight Into Terrain (CFIT) Education and Training Aid, produced jointly by the Flight Safety Foundation, Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO), CFIT accidents continue to occur worldwide. The article below, written by Captain Jim Gregory thirteen years ago and published in the Airspace Newsletter in 1998, is still pertinent.
CFIT Prevention Initiatives
I have had the opportunity recently to carefully review the Controlled Flight Into Terrain Education and Training Aid material produced and issued jointly by the Flight Safety Foundation, the United States Federal Aviation Administration and the International Civil Aviation Organization (ICAO). The information presented in this material is sobering, to say the least!
The Flight Into Terrain document is an extensive compilation of worldwide Transport Category Aircraft Controlled Flight Into Terrain (CFIT) accidents and events where the aircraft was either inadvertently flown into the ground, or nearly flown into the ground. It has detailed accounts of these accidents and incidents that should be required reading for ALL pilots who are currently flying in the world’s skies. The report makes one firmly convinced that Ground Proximity Warning Systems (GPWS) are worth their weight in gold (and maybe more) considering the number of times this system has SAVED the passengers, crew and aircraft. Other technical advances, such as enhancing GPWS, excessive bank angle warning devices, head-up displays, enhanced and synthetic vision and Minimum Safe Altitude Warning Systems (MSAW) for use by Air Traffic Control (ATC) to alert aircraft under their control of terrain proximity, are being developed and/or refined to provide that extra “last resort” warning to the flight crew in order to prevent a controlled flight into terrain accident. The Flight Into Terrain document also provides a “CFIT Checklist” or a CFIT risk-assessment safety tool as part of an international program to reduce CFIT accidents.
The international CFIT prevention initiatives are laudable and provide the framework for CFIT prevention activities to take hold. However, one aspect of the CFIT prevention initiatives that does not appear to be highlighted is the following question: Why are transport category aircraft flying at the minimum IFR altitudes on non-precision approaches (NPAs)?
Most CFIT Occurrences are on NPAs
It is said that transport category aircraft flying non-precision approach procedures account for most of the world’s CFIT related accidents. The point of impact of most CFIT accidents is in line with the intended runway for landing anywhere from one to several miles away from the runway. Why would a pilot (or crew) violate a minimum IFR altitude on an approach procedure to the point of colliding with the terrain?
Every IFR-rated pilot knows that a non-precision approach procedure is one where there is no procedure vertical guidance, and that all altitudes associated with the non-precision procedure are minimum IFR altitudes or “DO NOT DESCEND BELOW ALTITUDES”. All IFR-rated pilots also know that these minimum IFR altitudes are determined by the instrument procedure design specialist according to established criteria and standards wherein during the initial approach segment of the procedure (from the initial approach fix to the intermediate fix), 1 000 feet of obstacle clearance is provided above the highest obstacle within that segment; 500 feet of obstacle clearance is provided in the intermediate segment (from the intermediate fix to the final approach fix [FAF]); and, depending upon the type of facility the procedure is based upon, as low as 250 feet of obstacle clearance is provided in the final segment (from the final approach fix to the missed approach point). Refer to Figure 1.
Click on image to enlarge.
The procedure turn minimum IFR altitude of 1 800 feet provides 1 000 feet of obstacle clearance within a defined area for the procedure turn initial segment; the FAF minimum IFR altitude of 1 300 provides 500 feet of obstacle clearance in the intermediate segment (in this case, when the aircraft is established inbound on the 215 course within the procedure turn distance of 10 NM), and 250 feet of obstacle clearance in the final segment (from SELAT to the missed approach point, which in this case is the threshold of runway 22). Proponents of stabilized descent techniques, in which the pilot attempts to place the aircraft on a 3° descent path to a 50-foot threshold crossing height on non-precision procedures such as the one above, have argued that the approach slope in the final segment shown in Figure 1 above is very low and unacceptable for stabilized approach techniques. An approach slope may be calculated by taking the FAF minimum IFR altitude (1 300 feet) and subtracting the threshold elevation (459) plus a 50-foot threshold crossing height, and dividing the result by the distance from FAF to threshold (5.1 NM). The result is:
1300 - (459 + 50) = 791 / 5.1 = 155 feet per NM
or (155 / 6076.1 = .0255098 INV TAN) = 1.46°.
A 1.46° descent flight path is certainly not an acceptable way to fly a large aircraft to the runway! Since this is not acceptable, one has to ask the question why is the aircraft crossing the FAF at the MINIMUM IFR altitude of 1 300 feet? In order to have the aircraft established on a stabilized descent that approximates a nominal 3° descent path of a precision approach, the aircraft should be flown to cross the FAF at an altitude of no lower than 1 674 feet plus the elevation of the touchdown zone, or approximately 2 100 feet!
In most, if not all, circumstances an aircraft is probably already cleared for an approach by the time it reaches the FAF. In most, but not all cases, the aircraft is usually above the minimum IFR FAF crossing altitude when cleared for the approach. Why then, would a pilot wish to descend to a minimum IFR altitude at the FAF and expose the aircraft to a 500-foot obstacle clearance as well as expose the aircraft to a very shallow descent profile? Would it not be a better, and safer practice for the pilot to maintain an altitude ABOVE instead of driving the aircraft down to the minimum IFR altitude? If the pilot was to fly the procedure turn on the approach in Figure 1, how many pilots would descent to 1 800 feet within the turn? Why? ATC you say? Remember ATC is just as concerned about CFIT as the flyers therefore ATC will assist in any way that they can to contribute to a safe flight.
Minimum IFR Altitudes on Approach! Why Are You There?
I recall, when I used to instruct instrument procedures to IFR students, one student who was flying a procedure turn and was desperately trying to maintain the procedure turn minimum IFR altitude without much success. The student knew that he must not descend below (let us use our example in Figure 1) 1 800 feet during the conduct of the procedure turn manoeuvre, however, he was struggling to maintain that altitude—so much so that his cross-check suffered to the point that he lost situation awareness and got very confused as to where he was in the procedure turn pattern. We had received our clearance to the airport for an approach when we were about 20 miles inbound to the navaid at 4 000 feet so we had all of the altitudes from our present position at 4 000 feet all the way to the missed approach clearance limit altitude yet the student chose to descend immediately to an appropriate Minimum Sector Altitude (MSA) for the procedure and then immediately descend to the minimum IFR altitude for the procedure turn at the appropriate time.
When the student was questioned as to why he was operating the aircraft at a minimum IFR altitude he could not defend his actions by any reason other than to say, “ ...because that’s what is published.” It appears that many pilots view MINIMUM IFR altitudes on instrument approach procedures in the same way. Since the procedure designer determines these altitudes using established criteria and standards, and because these altitudes are published on the procedure, it seems that some pilots have this unexplainable urge to descend to these altitudes and subject the aircraft (and all who occupy it) to an altitude that is described in all IFR publications as, “ALTITUDES ARE MINIMUM ALTITUDES AND MEET OBSTACLE CLEARANCE REQUIREMENTS UNDER ISA CONDITIONS.” Not only are pilots forcing aircraft down to the minimum IFR altitudes on approaches, databases on modern aircraft flight management systems (FMS) also drive the aircraft to these minimum IFR altitudes. Instrument approach procedure altitudes are coded in the FMS as “HARD” altitudes thereby driving the aircraft to these altitudes whenever the aircraft is managed vertically by the FMS1.
Consider the certified maximum operating indicated airspeed on an aircraft. We all know that if we operate the aircraft at this maximum airspeed, it is certainly safe to do so. Some may refer to operating an aircraft to its capability as “operating at the envelope”. If we happen to unintentionally exceed this maximum, we also know that the aircraft does not instantaneously disintegrate. We assume that the flight test engineers have provided some margin of safety beyond the placard maximum, however we do not operate the aircraft at this maximum airspeed all the time. If we need it, we know that we can use it—safely. Can not the same logic apply to the minimum IFR altitudes on an approach procedure? If we do not need it, should we not operate the aircraft above the minimum IFR altitude? Really, the only minimum IFR altitude a pilot should operate an aircraft at, in IMC, is the Minimum Descent Altitude (MDA), and only if the weather conditions require it.
Rules of Thumb
There are a couple “rules of thumb” a pilot can use to determine altitudes along a final approach course to approximate a 3° descent flight path. Taking into account a necessary 50-foot threshold crossing height, a 3° descent path at 5 NM from the runway threshold is 1 642 feet above the elevation of the threshold. At 10 NM this same descent path is 3 234 feet above the elevation of the threshold. By adding the threshold elevation to 1 600 (1 642 rounded to 1 600) and 3 200 (3 234 rounded to 3 200), you can determine what the altimeter should read at these points along the final approach course. Applying this rule of thumb to our example in Figure 1, we can quickly determine that we should cross the FAF at approximately 2 100 feet on an altimeter correctly set to the local station altimeter setting. The long calculation is as follows:
FAF is 5.1 NM from the threshold
3° descent (with a 50-foot TCH) crosses 5.1 NM at 1 674 feet
add 459 (runway elevation) to 1 674 = 2 133 feet at the FAF
A “rule of thumb” application to the same problem follows:
at 5 NM from threshold, you should be at approximately 1 600 feet
add threshold elevation (459 feet rounded to 460) to 1 600 = 2 060 at 5 NM
because the FAF is a little farther than 5 NM (5.1 NM) correct the FAF crossing altitude to 2 100 feet.
The “rule of thumb” can be simplified by saying that to maintain a 3° descent flight path, for every NM along track distance you fly, you need to descend 318 feet. (You may wish to round this value to 300 feet of descent for every NM to help in quick calculations.)
These “rules of thumb” calculations can be accomplished during the flight planning portion of the flight and/or prior to the descent from the en route altitude, and included in the approach briefing. Let us return to the example in Figure 1. If we want to be on a stabilized approach on this procedure, we should cross the FAF at 2 100 feet - not 1 300 feet! There is nothing prohibiting any pilot from conducting a non-precision instrument approach procedure in this fashion. The published 1 300 feet at the FAF is a “DO NOT DESCEND BELOW” altitude and crossing the FAF at 2 100 feet certainly meets this requirement. Extending the rule of thumb to the 10 NM point, the aircraft should be at 3 200 feet + the threshold elevation (460) = 3 660 or rounded to 3 700 feet. Therefore, if cleared to the airport for an approach and you are required to fly a procedure turn, why not maintain 3 700 feet during the procedure turn rather than driving the aircraft down to the MINIMUM IFR altitude of 1 800 feet. The procedure turn must remain within 10 NM of the FAF, in our example, thereby leaving at least 5 NM of level flight at 3 700 feet before intercepting a stabilized 3° descent path. With the knowledge of your groundspeed, you can establish a rate of descent needed to intercept and maintain the 3° descent profile. A 2 NM per minute groundspeed (120 knots) will required a rate of descent of approximately 600 feet per minute.
If ATC should happen to provide vectors to the final approach course and assign an altitude below 3 700 feet, you have a couple of options available:
maintain the assigned altitude and intercept the 3° descent path closer to the runway threshold; or
request a higher altitude from ATC. In most cases, they would accommodate such a request.
Low Approach Slopes?
It is apparent that some transport category aircraft pilots may have misunderstood the application of minimum IFR altitudes on non-precision instrument approach procedures for a long time. CFIT initiatives that discuss some non-precision procedures as having very low approach slopes clearly indicate this misunderstanding. There is no such thing as a “very low approach slope” on a non-precision approach procedure. There ARE, however, minimum IFR altitudes that if honoured, will provide the aircraft, under ISA conditions, obstacle clearances determined by recognized criteria and standards. How, and why, pilots got the idea that they must be at the procedure minimum IFR altitude is puzzling.
We need to instill upon IFR pilots that the minimum IFR altitudes of a non-precision approach are just that, MINIMUM, and placing the aircraft at the procedure design minimum IFR altitude or “envelope”, while certainly safe to do so, may not be the wisest choice under all circumstances. Modern technology has provided the pilot with useful devices to help make the correct decisions, however, modern technology will never replace good pilot judgment. For those aircraft that have navigation databases wherein the approach procedure is coded into the database and presented to the pilot, the vertical information must be based upon a 3° flight path descent to a 50-foot TCH and not determined by the minimum FAF crossing altitude to ensure the required obstacle clearance which, in most cases, will establish descent angles less than 3°. Rules of thumb to calculate a stabilized descent profile on any non-precision approach procedure should be included in all preflight planning briefings as well as the approach briefing prior to descent. Placing the aircraft at the minimum IFR altitude on an approach should only be accomplished along the final approach segment (i.e., MDA) and only if required by the weather conditions. For example, flying at the minimum IFR altitudes on an instrument approach at night in clear conditions is not good airmanship.
Approaches Steeper than 3°
Most non-precision instrument approach procedures will accommodate a 3° descent profile, however some will not. See Figure 2.
Click on image to enlarge.
Here is a case where the “rule of thumb” of 1 600 feet above runway threshold elevation (181 feet) at 5 NM quickly shows that a descent profile of something greater than 3° is required for this approach. In fact, looking further along the final approach segment, the step-down waypoint minimum altitude restriction of 1 300 feet at 3 NM requires 373 feet per NM or approximately a 3.5° descent path. On this particular instrument approach procedure, a pilot may not have any choice but to fly at the minimum IFR altitudes on the approach in order to control the rates of descent.
All pilots need to reassess their reasons for operating aircraft at minimum IFR altitudes (procedure envelope) on approach. Is it necessary? Cannot the approach be successfully flown above all of the minimum IFR altitudes, especially if the weather conditions do not require the aircraft to be at MDA to establish the required visual references? Reassessing how pilots fly non-precision approach procedures will go a long way towards preventing CFIT occurrences.
About the author: Captain Jim Gregory was involved in aviation for more than 40 years, first as a military fighter pilot and instrument check pilot and subsequently as a Transport Canada (TC) airspace inspector. He became heavily involved in the development of instrument flight procedures and instrument procedure design standards both domestically and internationally, and he was a long-time member of the ICAO Obstacle Clearance Panel. Jim retired from TC several years ago and went to work for Bombardier Aerospace as a training pilot. Sadly, he passed away in the Spring of 2010 after a long battle with cancer. Per ardua ad astra. —Ed.
1 These statements reflected reality when this article was written in 1998. Nowadays, while most navigation data providers will code “at or above” altitude, there are still some original equipment manufacturers (OEM) that may code hard altitude. To know exactly what is coded in your box, you have to ask the manufacturer.
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