Frequently Asked Questions

A. Please contact us at to discuss pricing structure for your company’s needs.

A. At this time we only charge on a monthly subscription basis.

A. All of our subscriptions give access to our entire worldwide database of over 10,000 airports.        

A. The APG WB and iPreflight apps require one-time use codes for logging in on the iPhone/iPad. We will issue up to 4 codes per tail to access the account. Additional codes may be provided on a case-by-case basis. ATLAS and Web WB use one common login for each account.

A. APG subscribes to NOTAMs via the FAA Aeronautical Information Data Access Portal (AIDAP). However, with over 10,000 airports within the APG database, it is simply not possible to monitor NOTAMs on a daily basis. We instead ask customers to contact us, either by phone or email, when a customer encounters a NOTAM that they believe may impact performance. We will then analyze if the NOTAM will affect aircraft performance and will make the appropriate corrections if need be. We also have the ability for the user to interactively adjust runway lengths, if they encounter a NOTAM closing a portion of the runway. This is the “Shorten Runway” tool, and is available in all of our current product offerings.

A. No, there is a safety margin built into AFM performance data. This safety margin is outlined in Part 25 (Aircraft Certification), but involves a conservatism applied to the actual data gathered by the test pilots upon certification. This conservatism is accomplished in various forms, with the most commonly referred to being a Gross climb gradient reduced to Net climb gradient factor. This is a reduction in the actual aircraft’s climb performance as a function of the number of engines. The decrement ranges from 0.8% (2 engine aircraft) to 1% (4 engine aircraft) for first, second, and third segment climbs/acceleration. An example would be if you are clearing an obstacle by a NET 35 ft, and the obstacle is 2 NM off of the departure end of the runway, you will actually be clearing that obstacle by at least 135 feet. At 10 NM this becomes over 500 ft. To determine the actual aircraft height above the 35 foot NET height, simply multiply the gradient reduction, .008 for example, by the distance in feet, to the obstacle. Also, this is assuming the worst case scenario of losing the critical engine AT V1, continuing the takeoff, operating at the maximum weight allowed for that scenario, and the obstacle in question is the most limiting obstacle. If the engine failure occurs after V1, or you depart with a lower weight than the maximum for that scenario, you will further increase this safety margin.

A. APG does not provide this information within any of its applications. Providing this information to the end user promotes the practice of comparing the one engine inoperative second segment climb gradient to the TERPS/PANS-OPS all-engine minimum climb gradient required. This is not the intended means of meeting the FAR/EUOPS obstacle clearance requirements, and is a common misconception within the aviation industry. Please review the following FAQ, “Does APG’s data meet TERPS requirements?” for more clarification on the difference between TERPS and a proper Runway Analysis.

A. This is likely the most frequently received question at APG. The short answer is that no, our data does not specifically take into account, or meet, TERPS/PANS-OPS all-engine minimum climb gradients. A proper Runway Analysis using your Aircraft Flight Manual’s One Engine Inoperative performance data is required by the FARs, and is a more accurate, detailed analysis for the specific aircraft and situation you are operating with. TERPS climb gradients are based on normal, all engines operating, are not regulatory, and often ignore low close-in obstacles. Comparing TERPS gradients against OEI climb performance in the AFM’s performance section (typically second segment climb data) is not an overly conservative method of determining obstacle clearance. OEI runway analyses do not always meet TERPS requirements, nor are they required to. TERPS, on the other hand, do not guarantee that OEI obstacle clearance is met, and thus following TERPS climb requirements may not meet the requirements set forth by the FARs. Often times, TERPS requirements are set forth for noise abatement, ATC preference, navigational aide reception, etc. Here is an excerpt from Advisory Circular 120-91, explaining the difference between TERPS climb gradients and a OEI Runway Analysis:


a.  Standard Instrument Departures (SID) or Departure Procedures (DP) based on TERPS or ICAO Procedures for Air Navigation Services—Aircraft Operations (PANS-OPS) are based on normal (all engines operating) operations. Thus, one-engine-inoperative obstacle clearance requirements and the all-engines-operating TERPS requirements are independent, and one-engine-inoperative procedures do not need to meet TERPS requirements. Further, compliance with TERPS all-engines-operating climb gradient requirements does not necessarily assure that one-engine-inoperative obstacle clearance requirements are met. TERPS typically use specified all-engines-operating climb gradients to an altitude, rather than certificated one-engine-inoperative airplane performance. TERPS typically assume a climb gradient of 200 feet per nautical mile (NM) unless a greater gradient is specified. For the purposes of analyzing performance on procedures developed under TERPS or PANS-OPS, it is understood that any gradient requirement, specified or unspecified, will be treated as a plane which must not be penetrated from above until reaching the stated height, rather than as a gradient which must be exceeded at all points in the path. Operators must comply with 14 CFR requirements for the development of takeoff performance data and procedures. There are differences between TERPS and one-engine-inoperative criteria, including the lateral and vertical obstacle clearance requirements. An engine failure during takeoff is a non-normal condition, and therefore takes precedence over noise abatement, air traffic, SIDs, DPs, and other normal operating considerations.”

Now for the long answer. According to CFR Part 121.189 and CFR Part 135.379, “No person operating a turbine engine powered airplane may take off that airplane at a weight greater than that listed in the Airplane Flight Manual—“. This means that anyone who is operating an aircraft under Part 121 or Part 135 must abide by the performance section of their Aircraft Flight Manual (AFM). The performance section’s obstacle clearance requirements are governed by CFR Part 25 (Aircraft Certification), and are based on the worst case scenario of losing the critical engine at V1. For Part 91 operators, there is a little more of a gray area as to whether or not a complete runway analysis is required. If you are operating under Part 91, I recommend you read our other FAQ titled “I operate under Part 91; do I need to use APG’s runway analysis numbers?”. To summarize, Part 91 operators when flying in IMC conditions must fly a procedure that ensures obstacle clearance for the aircraft they are operating. The only way to ensure this obstacle clearance is met is to use a complete One Engine Inoperative runway analysis.

CFR Part 25 outlines the obstacle clearance requirements that are required to be included in the AFM. In summary, these require the aircraft to clear all obstacles by a NET 35 ft vertically, or by 200-300 ft horizontally, depending on if the aircraft is within airport boundaries or not. In 2006, Advisory Circular 120-91 was published to set a new standard for the width of the corridor in which operators should be considering obstacles, as well as clarify some misconception regarding TERPS vs Runway Analysis. This corridor is very similar to that found in Part 25, but it is slightly more conservative and allows for an aircraft to drift off of the intended flight path and still be within the corridor in which the obstacles were analyzed. Where this differs from TERPS is that TERPS is a general corridor based on numerous criteria such as wingspan, normal operating speeds (i.e. accelerating to 250 KIAS below 10,000 feet), available Navaids, terrain in the area, airport surveys, turning procedures, ATC, etc. TERPS is not based on an intended flight path for a specific aircraft and situation, but rather a large area that can accommodate everything from a C172 to an A380. Because of this, TERPS will often require a steeper climb gradient than is needed, to cover all possible intended tracks for the SID/ODP. In event of an engine failure, APG’s Runway Analysis assumes the pilot will maintain extended runway centerline track, or if an APG published Departure Procedure is used, APG assumes the pilot will follow that DP as described in the textual page that is accompanied with any data on a DP. This allows APG to meet all requirements set forth in the AFM for obstacle clearance, while utilizing the corridor specified in AC 120-91.

As mentioned in AC 120-91, another downfall to TERPS is that there is a stipulation that allows for certain low, close-in obstacles to be ignored from the calculation of a TERPS climb gradient. A prime example of this is at Teterboro Airport (KTEB) in New Jersey. At the time of this writing, when departing the Teterboro Eight Departure, the TERPS climb gradient required is 500 ft per NM, or about 8.2%. There is also a note that reads “RWY 6: Sign, poles, buildings, and trees beginning 235 ft from DER, 10 ft LEFT of centerline, up to 106 ft AGL.” Doing a little math, had these obstacles have been considered in the creation of this SID, the minimum TERPS climb gradient required would be approximately 2,750 ft per NM or 45%. Obviously this climb gradient would be impossible even with both engines operating, so the obstacles are removed from the analysis, and added in text form on the SID. But, according to the CFR’s and AC 120-91, you are required to clear all obstacles by a NET 35 ft within a corridor that is 200 ft either side of centerline. Given that this obstacle is listed at only 10 ft offset of extended centerline, it not only becomes a regulatory requirement, but also a safety requirement.

At APG, we take these obstacles into account, and determine if they fall within the corridor outlined in AC 120-91. If they do, we analyze the performance in such a way that will allow the aircraft to clear all known obstacles by the required 35 ft NET. In this particular case, an aircraft will likely never reach a 45% climb gradient, so weight is going to be reduced to a point at which the aircraft is able to complete the takeoff distance required prior to the end of the runway, thus giving the aircraft time to climb before the DER. This allows for a much lower minimum climb gradient required, but still ensures obstacles clearance requirements are met.

For more information on the subject, the following NBAA article also gives a detailed explanation of the difference between TERPS and Runway Analysis:

A.  This question is best addressed by referencing Advisory Circular 120-91:

“An engine failure during takeoff is a non-normal condition, and therefore takes precedence over noise abatement, air traffic, SIDs, DPs, and other normal operating considerations.

  1. In order for an operator to determine that a departure maintains the necessary obstacle clearance with an engine failure, the operator should consider that an engine failure may occur at any point on the departure flightpath.
    1. The most common procedure to maximize takeoff weight when significant obstacles are present along the normal departure route is to use a special one-engine-inoperative departure routing in the event of an engine failure on takeoff. If there is a separate one-engine-inoperative departure route, then the obstacles along this track are used to determine the maximum allowable takeoff weight for that runway.
    2. Consideration should be given to the possibility of an engine failure occurring after passing the point at which the one-engine-inoperative track diverges from the normal departure track. Judicious selection of this point would simplify the procedure and minimize the difficulty of this analysis. This is generally achieved by keeping the two tracks identical for as far as is practical.
    3. In some cases, two or more special one-engine-inoperative tracks may be required to accommodate all the potential engine failure scenarios. ” 

In general, when APG determines that a turning Departure Procedure is required due to limiting obstacles or terrain, APG will initially evaluate the published SID’s, ODP’s, or even the missed approach procedures for the chosen runway. If these procedures do not provide relief from the limiting obstacle/terrain, APG will then develop tailored Departure Procedures.

A.  “Declared distances represent the maximum distances available and suitable for meeting takeoff, rejected takeoff, and landing distances performance requirements for turbine powered aircraft. The declared distances are TORA and TODA, which apply to takeoff; Accelerate Stop Distance Available (ASDA), which applies to a rejected takeoff; and Landing Distance Available (LDA), which applies to landing. A clearway may be included as part of the TODA, and a stopway may be included as part of the ASDA.” (AC 150/5300-13A paragraph 323.a.)

  1. The takeoff decision speed (V1), and the following distances to achieve or decelerate from V1 are established by the manufacturer and confirmed during certification testing for varying climatological conditions, operating weights, etc.:
    1. Takeoff run — the distance to accelerate from brake release to liftoff, plus safety factors. (See TORA, paragraph 323.d(1).)
    2. Takeoff distance — the distance to accelerate from brake release past lift-off to start of takeoff climb, plus safety factors. (See TODA, paragraph 323.d(2).)
    3. Accelerate-stop distance — the distance to accelerate from brake release to V1 and then decelerate to a stop, plus safety factors. (See ASDA, paragraph 323.d(3).)
    4. Landing distance — the distance from the threshold to complete the approach, touchdown, and decelerate to a stop, plus safety factors. (See LDA, paragraph 323.e(1).)

For takeoff, APG analyzes the TORA, TODA, and ASDA distances. How these are handled vary depending on if the aircraft’s One-Engine-Inoperative (OEI) performance data is given as balanced or unbalanced field length data. In a balanced field length aircraft the performance data does not differentiate between accelerate-stop and accelerate-go distances. In an unbalanced field length aircraft, the accelerate-go and accelerate-stop distances are evaluated separately, as a function of the V1/VR ratio, and thus can be optimized for the particular scenario.

If the aircraft is balanced, the maximum distance available for takeoff, whether the takeoff is continued or rejected, is the lesser of the TORA, TODA, and ASDA. Since the accelerate-go and accelerate-stop distances are balanced, and thus equal to the field length required, exceeding any one of these three values would result in a longer field length required than available.

If the aircraft is unbalanced, the maximum distance for takeoff is separated on the basis of whether the takeoff was rejected or continued. If the takeoff is continued, the distance used will be the TORA, plus any clearway, up to the maximum clearway allowed. The maximum clearway allowable for use in calculating takeoff distances is defined in CFR 25.113 (c) (1) (i).

For takeoff on Wet runways, whether the aircraft is balanced or unbalanced, no clearway is allowed to be considered for takeoff. This means the aircraft must achieve the reduced 15 ft screen height by the end of the TORA. In addition, the use of reverse thrust may be considered for Wet runway performance.

For more information on the use of declared distances for takeoff in a One-Engine-Inoperative runway analysis, please refer to the performance section within CFR Part 25 (sections 101 thru 123).

Landing is a bit simpler, as the landing distance required must not be greater than the landing distance available, or LDA (refer to CFR Part 25.125). The landing distance required is based upon crossing the threshold at an altitude of 50 ft to a normal touchdown, maximum braking to a full stop.

A.  Some airports, especially in the United States, have an Accelerate Stop Distance Available that is shorter than the Takeoff Run Available. This is because the end portion of the runway is not available for accelerate-stop distance calculations, usually as a result of unacceptable land use in the Runway Protection Zone beyond the departure end of the runway. The FAA requires that there be a minimum ‘safety area’ beyond the departure end of the runway that is protected from infringement by items on the ground. This can include roads, buildings, farmland (that does not meet specific requirements), etc. More information can be found in AC 150/5300-13A paragraph 310 as to the requirements of this RPZ.

In the case of Teterboro (KTEB), at the time of this writing, there is an ASDA that is 910 ft shorter than the TORA on runway 01. This equates to an ASDA of 6,090 ft. Many charts in print today make no mention of this, and simply show a runway length of 7,000 ft with no restrictions to takeoff distance. This gives the illusion that the full 7,000 ft is available for takeoff, when in fact it is not.

The effect this has on performance will vary depending on whether the aircraft performance data given is balanced or unbalanced. If the aircraft is balanced, the maximum distance allowed for takeoff will be limited by the reduced ASDA. This is because a balanced aircraft by definition will have an accelerate-stop and accelerate-go distance that is equal (in most cases), and thus the calculated field length required must be less than or equal to the Accelerate-Stop Distance Available. If the aircraft is unbalanced, the aircraft must have an accelerate-stop distance that is shorter than the ASDA but the accelerate-go distance may exceed the ASDA. The maximum distance allowed for accelerate-go will be the TORA plus any clearway, up to the maximum clearway allowed. Refer to the above FAQ for further clarification on the use of clearways.

At the time of this writing over 250 airports in the United States have an ASDA that is shorter than the TORA. Some of the larger airfields include, but are not limited to:

  • Anchorage Intl (PANC)
  • Prescott (KPRC)
  • Fresno Intl (KFAT)
  • San Diego Intl (KSAN)
  • San Francisco Intl (KSFO)
  • Miami Intl (KMIA)
  • Orlando Intl (KMCO)
  • Tampa Intl (KTPA)
  • Atlanta Intl (KATL)
  • Savannah/Hilton Head Intl (KSAV)
  • Honolulu Intl (PHNL)
  • Chicago O’Hare Intl (KORD)
  • Peoria Intl (KPIA)
  • Minneapolis St. Paul Intl (KMSP)
  • Louis Intl (KSTL)
  • Teterboro (KTEB)
  • McCarran Intl/Las Vegas (KLAS)
  • Albany Intl (KALB)
  • Niagra Falls Intl (KIAG)
  • Rochester Intl (KROC)
  • Philadelphia Intl (KPHL)
  • Pittsburgh Intl (KPIT)
  • Dallas Love (KDAL)
  • Gen Mitchell Intl/Milwaukee Intl (KMKE)
  • Cheyenne Regl (KCYS)

A.  The Approach Climb limits published on all APG landing gross weight charts are taken directly from the approach climb (Landing WAT) information in the AFM. The ONLY regulatory requirement from initial aircraft certification is that the two engine aircraft is able to maintain a 2.1% climb gradient in the missed approach configuration of gear-up, one engine inoperative, go around power and flaps. This requirement is totally independent of the approach/missed approach being flown and any obstacle/terrain considerations.

Therefore, there is no consideration of obstacle clearance for the missed approach being flown.

Many airlines do recommend flying a takeoff Departure Procedure as the missed approach if there is one available for the runway in use and train in those scenarios. It seems better to follow a procedure where obstacle/terrain clearance has been considered than not.

Keep in mind that if you do intend to fly the takeoff Departure Procedure for a missed approach, the takeoff Departure Procedure would commence at the departure end of the runway and not necessarily from the missed approach point which, as you may realize, may be at some point still quite a distance from the arrival end of the runway.

A.  This is because these corrections are generic and must apply to all temperatures listed on the analysis. Essentially the program calculates the performance with zero wind and a QNH of 29.92, without any additional options selected (the limit weight shown in the middle of the page). Then the program will run the worst case scenario for wind, QNH, Bleeds, Anti-Ice, etc. and determine the correction to be made at each temperature listed on the report. Then, it selects the one correction value for each option that is the most limiting. This means that for most circumstances the correction factors will be at least a little conservative so that they can apply to all cases. Because performance degrades with an increase in altitude, often times the most limiting correction will be one that applies to one of the higher temperatures. This is not a steadfast rule, but rather a generalization. If you run a full temperature spread report, and need those few extra pounds, you may benefit from running the report at the actual temperature that day. This will often, but not always, yield lower correction penalties.

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