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Determining the climb gradient performance for a departure begins with clarifying the vernacular between:

A) what the aircraft is actually capable of doing (actual) and

B) the regulatory or physical gradient (required). 

The actual climb gradient is based on atmospheric conditions, take-off weight and aircraft configurations, such as flap setting, slots etc, whereas the required gradient  is based on aircraft certification, regulation and obstacle clearance.  We will consistently identify the gradients using italicized labels of actual and required, so as to reduce confusion throughout the discussion.

Under visual rules, pilots may not concern themselves with climb gradients as long as obstacles can be visually circumnavigated; however, even without the presence of obstacles, the aircraft must still be able to meet or exceed jet aircraft certification climb performance.  In other words, a two engine aircraft must be able to meet, with one engine inoperative, a minimum required gross gradient of 2.4% (3 engine aircraft 2.7% and 4 engine 3.0%).  We will discuss gross versus net in a bit, but notice that this is the required gradient.  Many manufacturers include a Max Weight Climb chart to determine if this most basic criteria can be met.  If one is not available, then the aircraft's 2nd segment climb charts must be visited and the pilot must make the appropriate adjustments for gross versus net.

If the flight is to be conducted under IFR, then a decision tree logic must be applied.

First, is a departure procedure or SID established for the runway to be used?

If yes, then FAA TERPS criteria establishes the required gross gradient.  As a minimum, we are familiar with the 200 feet per NM requirement; this translates to a 3.3% gradient (200 ft / 6060 ft/NM).  Since most depart plates describe the required gradient in terms of feet/NM, the pilot must make the conversion to a percent gradient.

If a departure is not established, then the pilot must determine the obstacle clearance gradient as described below; but first let us discuss gross versus net gradients.

GROSS versus NET

When the government determines minimum climb performance for aircraft certification or departures, they add a "fudge factor" to compensate for pilot reaction time, aircraft complexity etcetera.  The actual calculation of this factor involves complex formulations of obstacle penetration of planes extending varying degrees from the departure path. Suffice it to say, that the 200 ft/NM gradient includes governmental "fudge factors" for safety, therefore the value is gross. In fact, aircraft certifications (remember the 2.4% spoke of earlier) also contain "fudge factors" and are also gross requirements.  The government wants the aircraft to be able to actually fly at least as well as these values, with one engine inoperative. 

Before we speak of how the pilot compares chart data with these required values, let us look at the other situation.  When a departure procedure is not established for the runway.  Here the pilot must determine if the aircraft can clear an obstacle that lies within the departure corridor if an engine should fail.  This becomes a bit more involved and provides the basis for how actual numbers are compared to required gradients.

The required net (no government "fudge factors") 2nd segment climb gradient is calculated by determining the rise in altitude from a reference point above the end of a runway to the top of the obstacle.  If an aircraft were precisely able to maintain this gradient, it would "scrap paint" as it passed over the obstacle.  The government therefore would like to "fatten" up this requirement ("gross-ify" it if you will) by imposing regulation that requires 135 operators to clear the obstacle by 35 feet and also by adding its "fudge factor" to all operators.  That factor is 0.8% for two engines, 0.9% for three engines and 1.0% for four engine aircraft.

Lets look at an example; an obstacle is 140 feet above the runway and 2000 feet from the runway end.  The reference point above a dry runway is 35 feet (15 feet for a wet runway, effectively increasing the required gradient). Therefore, the geometric rise of 115 feet (140-35) divided by the run of 2000 feet renders a required net gradient of 5.75%.  Add in the Part 135 requirement (35 feet clearance) and the resulting required net gradient is 7.0%.  Assuming a twin engine jet, the required gross gradient becomes 7.8%.

Now that we know what minimum performance we must meet, we turn to the performance charts to determine the actual climb gradient of the aircraft under our specific take-off weight and atmospheric conditions.  Most 2nd Segment Climb charts are presented with Net results.  This means that the 0.8% "fudge factor" has been subtracted from the actual performance of the aircraft.  The pilot must carefully compare "apples and apples".  Directly comparing the results from a Net 2nd Segment chart to required gross gradients (such as when departure procedures exist) will be conservative because the "fudge factor" has been added twice. 

Additionally, some manufacturers calculate the 2nd Segment climb performance from the wheels up and locked altitude versus the 35 foot reference point.  Comparing the required gross gradient from our calculation above, to an actual gradient using this higher reference point results in a conservative comparison.

This discussion does not address Vmbe limitations, unbalanced field lengths or other factors addressed individually within the operating manuals.

QUESTION: If I am type rated in two aircraft (i.e. Challenger and Falcon), can I use my night currency in the Challenger to fly the Falcon at night?

ANSWER: Yes, if you meet the following:

1. You are not operating under parts 121, 125 or 135.  In other words, you're operating under part 91  [61.57 (e)(1) and (2)]

2. The type certifications are for aircraft that require more than one pilot.  [61.57 (e)(3)]

3. You hold at least a valid commercial pilot certificate. [61.57 (e)(3)(i)]

4. You have logged at least 1500 hours total time [61.57 (e)(3)(ii)]

5. You have logged at least 15 hours within the last 90 days within the Falcon.  [61.57 (e)(3)(iii)]

6. You are either:

   night current in the Challenger through three (3) actual take-offs and landings to a full stop within the preceding 90 days  [61.57 (e)(3)(iv)(A)]

    

   OR

night current in the Challenger through six (6) level C or D Challenger simulator take-off and landings to a full stop within the preceding 12 months [61.57 (e)(3)(iv)(B)]

 

ANSWER:

ANSWER: Any published (approved) instrument procedure that utilizes a:

If the approaches are performed within an approved simulator or flight training device, an authorized instructor (CFII or Instrument Ground Instructor) must be present.

Flying beyond the FAF and going missed or completing the approach visually ("breaking out") prior to the decision height or MDA is considered a "concluded" approach and appropriate for logging.

61.57(c) Instrument experience. Except as provided in paragraph (e) of this section, no person may act as pilot in command under IFR or in weather conditions less than the minimums prescribed for VFR, unless within the preceding 6 calendar months, that person has:

(1) For the purpose of obtaining instrument experience in an aircraft (other than a glider), performed and logged under actual or simulated instrument conditions, either in flight in the appropriate category of aircraft for the instrument privileges sought or in a flight simulator or flight training device that is representative of the aircraft category for the instrument privileges sought --

(i) At least six instrument approaches;

(ii) Holding procedures; and

(iii) Intercepting and tracking courses through the use of navigation systems.

ANSWER:

ANSWER: Mean Sea Level (MSL) is a local tidal datum which is determined by averaging the hourly height readings over a specific 19 year period.

NOS operates a network of water level stations for which those local datums are determined.

The term MSL has also been confused  with the geodetic datum, National Geodetic Vertical Datum of 1929 (formerly called the Sea Level Datum of 1929).  It has appeared and may still appear on outdated maps or references to land based topographic elevations as the geodetic datum zero.  It was originally based on local mean sea level measurements at  26 tide stations in the US and Canada and adjusted in the year 1929.

The geodetic datum, NGVD is a fixed datum, while MSL is not.

Steve Lyles, National Ocean Service

ANSWER: The standby instrument does not take into account compressibility.
Compressibility increases with altitude.

ANSWER: ADC's compensate for compressibility and instrument error. ADC will also
compensate for density altitude, and it will display TAS in another location
(ie. MFD or separate SAT/ TAS gauge).

QUESTION:  What are special airworthiness certificate in the limited, restricted, experimental and primary categories?

ANSWER: The Limited certificate is issued to operate surplus military aircraft that have been converted to civilian use under the following conditions:

FAA Order 8130.2 contains a list of aircraft models that have been issued limited category type certificates.

Primary category aircraft are of a simple design and intended exclusively for pleasure and personal use.  Although these aircraft may be available for rental and flight instruction under certain conditions, the carrying of persons or property for hire is prohibited.  

Aircraft certificated in the primary category must be manufactured under a production certificate.  This includes aircraft assembled from a kit under the production certificate holder's supervision and quality control system.  Kit-built aircraft built without the production certificate holder's supervision are only eligible for certification in the experimental category (see below).

Restricted category aircraft is limited to special purposes identified in the applicable type design.  These special purpose operations include the following:

The Experimental certificate is issued to operate an aircraft that does not have a type certificate or does not conform to its type certificate.  Additionally, this certificate is issued to operate kit-built aircraft that were assembled without the supervision and quality control of the production certificate holder.  Special airworthiness certificates may be issued in the experimental category for the following purposes:

ANSWER: No.

Ref. §61.57(c) and (d); A person may not act/serve as PIC under IFR or in weather conditions less than the minimums prescribed for VFR if he has not accomplished the instrument currency tasks of paragraph (c) of § 61.57 within the preceding 6 calendar months. The way to read §61.57(c) and (d) is as follows:

In order for a pilot to act/serve as PIC under IFR or in weather conditions less than the minimums prescribed for VFR, that pilot a person must have ". . . performed and logged under actual or simulated instrument conditions, either in flight in the appropriate category of aircraft for the instrument privileges sought or in a flight simulator or flight training device that is representative of the aircraft category for the instrument privileges sought--

(i) At least six instrument approaches;

(ii) Holding procedures; and

(iii) Intercepting and tracking courses through the use of navigation."

Otherwise, the pilot should check their logbook to find that it shows the following instrument currency tasks performed within the preceding 6 calendar months:

(i) At least six instrument approaches;

(ii) Holding procedures; and

(iii) Intercepting and tracking courses through the use of navigation systems.

Our example:

An IFR flight is proposed on the 15^th of September. The pilot would check for the required instrument currency experience back as far as the first day of March [i.e., as per § 61.57(c) ". . . within the preceding 6 calendar months, that person has . . ."] emphasis added "calendar months." In this scenario, ". . . within the preceding 6 calendar months, that person has . . ." equates to experience for the requirements logged up to 204 days previous, rather than just 180 days, because as per § 61.57(c) ". . . within the preceding 6 calendar months, that person has . . .". However, if for instance only 5 approaches had been logged during this period and the first of the required 6 approached had been logged on February the 28^th the pilot could not file the flight plan and be able to act/serve as the pilot-in-command under IFR or in weather conditions less than the minimums prescribed for VFR. His currency for this purpose would have ended on August 31.

Now, in our example, if the first of the usable five approaches had been logged, lets say, on the 10^th of June and the holding/intercepting requirements had been met since then, our pilot could not act as PIC, but he is "within 6 calendar months after the prescribed time" (the second six months). As soon as he makes at least one additional instrument approach (actual or simulated conditions) his currency for acting (serving) as PIC suddenly jumps to December 31st, representing 6 calendar months from June 10 through December 10 and actually to the end of December.

If our pilot had logged all of the 5 approached in June and did not have the opportunity to do any further instrument flight on or before the last day of June the next year, our pilot would now be required to meet the instrument proficiency check requirements of §61.57(d). And then the clock starts all over again (i.e., first six calendar months, second six calendar months, and IPC).

If our pilot had 1 approach/month, with the first in April AND did not have the opportunity to do any further instrument flight on or before the last day of of March the following year, our pilot would now be required to meet the instrument proficiency check requirements above.

What you expect to fly in the future is irrelevant.

ANSWER: Actually,

The 2.4% mentioned has nothing to do with the 2nd Segment climb.  It refers to the certification of transport category aircraft with 2 jet engines in particular.  That type of aircraft must, with one engine inoperative, be able to climb to 400 ft with flaps in the takeoff position at no less than a 2.4% gradient. 2nd Segment typically goes to 1500 and flaps can be retracted before 400 feet.  Three engine is 2.7% and 4 engine is 3.0%.

The 3 and 4 engine differences comes into play by a requirement in the General section of FAR 25;

(h) The procedures established under paragraphs (f) and (g) of this section must—
(1) Be able to be consistently executed in service by crews of average skill;

(2) Use methods or devices that are safe and reliable; and

(3) Include allowance for any time delays, in the execution of the
procedures, that may reasonably be expected in service.

(i) The accelerate-stop and landing distances prescribed in §§25.109 and
25.125, respectively, must be determined with all the airplane wheel brake assemblies at the fully worn limit of their allowable wear range.

The FAA decided that to meet these requirements, that aircraft with more engines, usually heavier, longer accelerate-stop distances needed to be able to climb at the higher gradient.

Keep in mind, that minimum SID requires 3.3% or higher.  So your Max Wgt for Climb charts only confirm basic aircraft certification.  To ignore, or not calculate this value, if such a chart exists for your aircraft, is to run the risk of taking off with conditions that do not meet the aircraft's certification, i.e the aircraft is not airworthy.  You then need to confirm that you can make the SID by comparing the 2nd segment charts (or better yet SID climb charts if available). 

Remember to compare Gross gradients (SIDs) with Gross (not Net) performance charts.
 

So what’s going on with the latest advisory circular on weight & balance?  Well, first, for whom is AC120-27E intended?  In a word, everyone. The circular clearly states that the process described within is applicable to part 91, 91k, 135 and 121, but unless you operate in the realm where Advisory Circulars are law, the eighty page document is advisory in nature only. If you choose not to follow the circular, understand that the FAA, under current regulations can, and probably will, ask you to demonstrate how the center of gravity is maintained within the operational envelop during the ENTIRE flight. AC120-27E is a product of recommendations from the NTSB after a commuter aircraft crash in South Carolina.  Even though W&B played only a minor role in the incident, the NTSB made several observations that current loading procedures, do not take into consideration, passenger, crew and equipment movement during flight.  So right out of the chute, even if you use actual weights, if passengers or crew have the opportunity to move about during flight, you are affected by this circular.

Two other factors which were identified that could potentially be problematic are the use of standard or segmented weights and non-assigned seating. Ultimately, the FAA solution to these recommendations involves curtailing (trimming down) the CG envelop. The crew and passenger movement factor is a fairing straight-forward adjustment, but the later two methodologies require a more elaborate correction involving statistical sampling and adjustments to the CG envelop. Each adjustment is cumulative, in other words, each curtailment is on top of the previous adjustment.  So, if you plan on using segmented weights, unassigned seating in a cabin with a lavatory, then be prepared to greatly reduce the operational CG envelop of your aircraft.

Since all piston and single engine turbine aircraft are prohibited from using anything other than actual weights, their only consideration, and the first consideration for everyone else, is crew, passenger and equipment movement within the cabin.  The idea is to determine the most extreme and probable change in CG by the movements.  Assuming that the aircraft manufacturer did not already curtail the envelop during certification to account for passenger movement, then the moment change for, lets say, a crew member moving to an aft lavatory, must be added to the total aircraft takeoff moment.  If the resulting CG falls outside the envelop then this would be a potentially adverse condition.  So the moment adjustment must be translated to a CG arm restriction in order to keep the loaded CG from falling too close to the aft limit. Other common movements might be passengers moving from the aft seats to the jumpseat or galley.  Though not mentioned within the circular, operational limits can be addressed within the ops spec that would make certain movements unlikely, such as "No passengers allowed into the galley for twenty minutes after takeoff or until the fasten seat belt sign has been extinguished".  This approach would require FSDO approval and appropriate justification, i.e. twenty minute fuel burn would eradicate the potential CG violation of the limits due to the passenger movement.  These extreme movements may be found within the loading documentation of your aircraft, but if not, one must be determined for your unique interior design.

The use of standard or segmented weights adds another level of uncertainty to the loading equation.  Standard weights have been identified by the FAA through a survey conducted by the Center for Disease Control.  While you are not required to use these values, the alternative is to conduct your own survey with the sample size numbering more than two thousand passengers.  This, therefore, would only be recommended if your particular operation routinely and pervasively involved passengers not meeting the FAA criteria.  To their credit, the FAA filtered through piles of statistical studies and created subsets of "passengers" who where adult versus children and further divided the adult group into male and female subsets.  Members of each group who fell well outside the mean were removed.  Crew member weights on the other hand came from first and second class medical records.  Baggage and carry-on weights were derived from several airline studies. 

So why, you might ask, if we are using these standard weights must the operational envelop be curtailed further?  Well, you have probably heard the adage, "there are lies, damn lies and then there are statistics".  Statistics are only 100% reflective of the entire population when you sample the entire population.  This obviously is not practical and the reason we have statistical analysis at all.  As you sample fewer and fewer people, the confidence level one has in the results, of accurately describing the population, becomes less and less. Ultimately, our goal is to make a statement of fact (the average weight of our passengers) based on the average of a very large group of passengers.  The more people in each group, the better the two will match.  Therefore, a large aircraft with several hundred passengers, will have an average weight that is statistically more reflective of the entire population than an aircraft with only four passengers.  So, even though we are both using the same standard weight for a passenger, the likely hood that a small aircraft actual average weight will vary from the entire population is greater.  It is this uncertainty that the FAA wants factored into your operational CG envelop. One more thing, even with the curtailments described above, there must be a procedure in place to override an obvious non-standard passenger weight.

The third factor has to do with how passengers are seated within the cabin.  When passengers are not assigned seats, there is a seemingly endless number of seating combinations, i.e. passenger A in seat one, passenger B in seat 2 and so on. To get a manageable handle on these possibilities, we are allowed to make assumptions to eliminate those possibilities that are not probable. For instance, it is highly unlikely that a sole passenger onboard would sit in the lavatory.  Airlines, for years, have used a widely accepted assumption called the "window-aisle-remaining" method.  Passengers are assumed to take the nearest window seat, then the nearest aisle seat and then those remaining.  The statistics and subsequent curtailment of the envelop to accommodate this seating flexibility probably does not warrant its use in small cabin aircraft, particularly if the inconvenience of using the actual seat assignment can be minimized.

Obviously, due to the mathematical gymnastics involved, the old style manual loading manifests and wiz-wheels will soon reveal themselves as burdensome. EFB-Pro with the Standard Weight module simplifies the assignment of seats.  In fact, passenger seating adjustments can be performed and the entire W&B recalculated on-the-fly without undo inconvenience or even awkwardness. The program automatically uses one envelop when using actual weights and another when using standard weights.  As male, female and children counts are exact, then a smaller curtailment is required than if the FAA's standard passenger (gender neutral) weight is used.  If all actual weights are used, then the envelop reflects only passenger movement curtailments.  The fuel burn CG is graphically overlaid on the operational CG envelop from takeoff to zero fuel weight (actually reserve fuel only weight), thus no further curtailment is required.  While this article does not go into the detail necessary to actually create the curtailments discussed, CAVU Companies is available to assist any operator.