Runway Declared Distances

All FAR Part 139 certificated airports have been updated to provide runway declared distances.  What are these declared distances and how are they applied to everyday flying.  Unfortunately many professional pilots haven’t kept up with the latest information from the FAA and could be in violation if they takeoff from a runway with a takeoff distance greater than these values.  We will take a look at each of the four declared distances and see how they are applied practically to a flight.

  • Takeoff Run Available (TORA) value:  The runway length declared available and suitable for the ground run of an airplane taking off.

  • Takeoff Distance Available (TODA) value: The takeoff run available plus the length of any remaining runway or clearway beyond the far end of the takeoff run available.

  • Accelerate-Stop Distance Available (ASDA) value: The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.

  • Landing Distance Available (LDA) value:  The runway length declared available and suitable for a landing airplane.

Definitions taken from FAA Pilot / Controller Glossary.

These declared distances can be found in the A/FD.  Here is an excerpt for Four Corners Regional Airport in Farmington, NM (KFMN).

KFMN AFD Excerpt

All multi-engine aircraft have two calculations to perform for their takeoff distance.  They are required to determine the accelerate-go distance and the accelerate-stop distance.  Just like the names imply, it is the distance required to either continue the takeoff or abort the takeoff, respectively.  Depending on the regulations the airplane was certified under, Part 23 or Part 25, determines the height of the airplane at the end of the accelerate-go distance.  Part 23 certified aircraft must climb to a height of 50 feet while Part 25 aircraft, 35 feet.

We use these takeoff performance numbers and they must be lower than the respective runway declared distances.  Accelerate-go must be lower than the TODA value and the accelerate-stop distance must be lower than the ASDA value.  As a side note, those aircraft that use a balanced field length single takeoff distance number must be lower than both the TORA and ASDA values.

Why can’t we use the whole length of the runway anyways?  Why do we need to have declared distances?  Good question.  A Boeing 737 landed fast in Burbank, CA and overran the runway.  It went through the metal blast fence and an airport perimeter wall coming to rest near a gas station.  This is one accident in many where the aircraft departs the end of the runway.

The FAA has determined in AC 150/5300-13 Airport Design that not all pilots are able to stop on the runway while either taking off and aborting the takeoff or landing.  To make this safer for the pilots and passengers they have created runway safety areas (RSA).

A runway safety area or runway end safety area (RESA) is defined as “the surface surrounding the runway prepared or suitable for reducing the risk of damage to airplanes in the event of an undershoot, overshoot, or excursion from the runway.

If the runway doesn’t have the required RESA, the airport operator could install an engineered materials arresting system (EMAS).  An EMAS system is defined as high energy absorbing materials of selected strength, which will reliably and predictably crush under the weight of an aircraft.

Photo of Functional EMAS Bed - NTSB Docket Photo

Picture taken from FAA Lessons Learned Website.

EMAS systems are shown on Airport Diagrams

KMDW Airport Diagram

As a result, every Part 139 certificated airport is required to have a RESA or EMAS system installed.  See the ends of runway 4R and 22L, 13C and 31C at Midway.  Some airports cannot expand the RESA past the end of the runway so they take the 1,000’ required for the RESA from the end of the runway.  This is easily seen in the TORA value.

I think we learned something here,  The TORA value may not equal the runway length.  In fact, the definition for TODA implies this.  The length of the usable runway may not be the actual pavement length of the runway.  Amazingly enough most of the professional pilots use Jeppesen plates and on their 10-9 chart will show takeoff and landing lengths.  These are necessarily equal to TORA and LDA, respectively, but they are close enough (within 1 or 2 feet) from what I can find.  As a result, I treat those values, takeoff as the TORA value and LDA and the landing value.  What you won’t find on Jeppesen charts legend is the ASDA value.  We have already shown that multi-engine aircraft must have a takeoff distance less than the TORA, TODA and ASDA value.  See KTUS, KTVL, KSAN for TORA values less than runway lengths.  These are only three of many more.


See page 65 of the Jeppesen Glossary Legends Manual.

So the question becomes, are there any airports where the ASDA is lower than the TORA.  The answer is yes.  In fact, Four Corners regional has one such runway.  Runway 7 and 25 have ASDA values lower than the TORA value.  See the picture at the top.  Are there other runways.  YES!

I was able to download the FAA airport and runway information text files.  I put those text delimited files into my favorite database program and learned there are over 2,300 airport where declared distances have been created.  Of those runway 324 have an ASDA shorter than the TORA value.  If you fly with Jeppesen charts, you can potentially takeoff overweight, which I am sure, at least in my airplane flight manuals, makes it illegal.

When I downloaded the FAA airport and runway information, I have found inconsistencies with the data displayed there and the AF/D.  For example, the AF/D shows KFMN above with ASDA lower than TORA values but you won’t find that airport in my spreadsheet.  The chart below won’t be kept up to date so, in all cases determine the declared distances from the proper sources.  The table below lists all the runways where the ASDA is more than 10% shorter than the TORA value.


Download the XLS file here

As a recap, declared distances are important for pilots to use while calculating takeoff and landing performance.  Understanding how they play into the performance calculation is key.  Without a proper understanding, pilots can cause unnecessary damage to their airplane, passengers and other on the ground by taking off at a weight greater than allowed.

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Cold Weather Airports in the United States

Finally!  After wishing the FAA would follow the lead of our friends to the north concerning errors associated with the altimeter and colder than standard weather we have a listing of airports that are required to temperature compensate their altitudes when the temperature is below a certain threshold.

Please read the notice to airman concerning the change.  Here

Background: In response to aviation industry concerns over cold weather altimetry errors, the FAA conducted a risk analysis to determine if current 14 CFR Part 97 instrument approach procedures, in the United States National Airspace System, place aircraft at risk during cold temperature operations. This study applied the coldest recorded temperature at the given airports in the last five years and specifically determined if there was a probability that during these non­standard day operations, anticipated altitude errors in a barometric altimetry system could exceed the Required Obstacle Clearance (ROC) used on procedure segment altitudes. If a probability, of the ROC being exceeded, went above one percent on a segment of the approach, a temperature restriction was applied to that segment. In addition to the low probability that these procedures will be required, the probability of the ROC being exceeded precisely at an obstacle position is extremely low, providing an even greater safety margin.

For most professional pilots compensating for temperature is as easy as turning the feature on in the flight management system (FMS).  For general aviation pilots, we must use the chart provided in the AIM 7-2-3.

Cold Temperature Correction Chart

To use this chart, you must know the temperature at the airfield through a weather report and you must know the AGL altitude for each of the segments you are going to use to fly the approach.  For example, on a standard ILS with a 5NM final approach fix the AGL height leading up to the FAF is 1500 feet.  If the temperature was
-20°C it is likely the aircraft is 210 feet lower than where it should be. To comply with the new notice to airman, the pilot should elect to fly 1,710 feet AGL instead of 1,500 AGL.

Pilots must report cold temperature corrected altitudes to Air Traffic Control (ATC) whenever applying a cold temperature correction on an intermediate segment and/or a published missed approach final altitude. This should be done on initial radio contact with the ATC issuing approach clearance. ATC requires this information in order to ensure appropriate vertical separation between known traffic. Pilots must not apply cold temperature compensation to ATC assigned altitudes or when flying on radar vectors in lieu of a published missed approach procedure. Pilots should query ATC when vectors to an intermediate segment are lower than the requested intermediate segment altitude corrected for temperature. Pilots are encouraged to self-announce corrected altitude when flying into uncontrolled airfields.

The FAA has listed 283 airfields as cold weather airfields with 307 different segments.  The segments that must be corrected are intermediate, final and missed approach.  There are 24 airports that have multiple segments listed.

States Map

The picture above shows the number of segments that must be temperature corrected in each state.  No surprise that Alaska has 87 different segments.  Another interesting fact is that all airports are above the 35° latitude line.

Alaska MapUS Map

There are quite a few airports where the temperature compensation is required and a current listing can be located on the Terminal Procedures Basic Search page on the Aeronav website.  A link directly to the PDF.

Table of AirportsThe temperature listed is where compensation needs to take place.  It may very well be different temperature than those listed on RNAV GPS approaches in the notes section.  Both must be complied with.

In future changes to the approach plates a “snowflake” symbol will be used to identify airports where temperature compensation must take place.  It will be the pilots responsibility to apply the correct compensation and inform ATC of the new altitude that are going to be used.


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Oh Those Wonderful Rules of Thumb

There are many rules of thumb in the aviation industry.  Things that we take for granted that our flight instructor told us to use but never explained why those rules of thumb really work.  Why do we descend at 450 ft/min when on a glideslope in small airplanes?  Where did that come from.  How about this rule of thumb: For every dot deflection on the VOR it is equal to 200 FT per NM.

I want to explore these rules of thumb and if there is one you would like me to research please leave a comment below.

2 degree pie sliceFor every dot deflection of the VOR CDI needle we are 200 FT / NM off course.  On the right is a circle representing the VOR signal emanating from the station.  We have a 2° slice from the circle representing one dot deflection and we want to know how long the yellow segment is.

Notice that this is not a right triangle so we cannot use standard right triangle formulas of Sin(Angle) = Opposite / Hypotenuse.  Time to pull out the trigonometry.  We know the lengths of the white segment and they are equal: 1NM or 6076.1 feet and we know the angle of 2° for one dot deflection.  The Side-Angle-Side formula will get us our result.

VOR 2 degree Deflection

As it turns out, every dot deflection of the CDI on the VOR is exactly 212.09 FT if you were 2° or one dot deflection on the VOR CDI.  This isn’t the whole story.  If we were 180° from our intended course we would be at least 2NM off course.  The deflection must change depending on the number of degrees we are off course.

VOR Deflection Graph 1

It turns out that 212 FT works really well if you are 2° off your course.  If you were 90° off your course then the 212 feet per dot per NM miles turns into 190.95 feet per dot per NM.  Does this really matter?  Let’s explore the difference we get from our rule of thumb versus the extremes of 2° and 90° off course.  The next graph shows the dot deflection using 190 FT, 200 FT and 212 FT for each NM from the station if we are 5 NM off course.

VOR Deflection Graph 2

We can see that with such a distance off course and as we get closer to the station the lines diverge.  We may only be 7 dots deflection off while we calculate 7.5 dots deflection.  That is not that big of a deal.  As pilots we like things really easy and 200 feet is much easier to calculate than 190 or 212 feet.  In the end, that average is good enough to keep us where we want to go.

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