How Do We Compare?

One of the most frequently asked questions we receive is “How does EFB-Pro compare with UltraNav?”.  The very short answer would be; EFB-Pro follows the AFM procedure for determining obstacle clearance and UltraNav does not.  We do not make this statement lightly or recklessly.  After numerous discussions with manufacturer representatives, simulator training instructors and close examination of the various AFMs, we are able to itemize five major differences between UltraNav and EFB-Pro as it relates to climb gradients and max allowable T/O weight.  Where available, we have included information directly from the UltraNav website to support our assertions. 

1.     Engine Max T/O thrust time is treated as the controlling factor for the 2nd segment within UltraNav. In other words, the required gradient is increased until the aircraft can top the SID within the 2nd Segment. When running UltraNav, the user will see an onscreen prompt that this is occurring. This results in a very limiting max T/O weight for the initial segments. EFB-Pro uses the 5 minute limit to determine the need to transition above or below an obstacle (i.e. can the obstacle be cleared by extending the 2nd segment, at max power, up to the 5 min limit or is it required to limit the weight for a higher 2nd segment with a transition segment?). Refer to the picture from UltraNav website below. Text in Times Roman font accompanies the picture from the UltraNav website.

2.    UltraNav makes no distinction between a SID requiring a 200ft/nm climb to 1000ft above the runway and a 1000ft obstacle 5NM (30000ft) away.  Both are treated as a 3.3% required gradient rendering exactly the same results (max T/O weight).  The problem is, one is gross and one is net.  This results in a very weight limited SID departure under all circumstances since the 2^nd segment charts are Net. Thus the safety margin of the SID (.8%) is added to the safety margin of the net charts (.8% -1.0%) which is essentially a “doubling-up” of the safety margins.  Also, using the unmodified SID as the required gradient criteria does not allow for a 35ft clearance along the entire path per 135 regulation.  EFB-Pro reduces the SID gradient by .8% and raises the reference point from 35ft to 70ft (thus slightly reducing the available runway length), then applies the Net performance charts of the aircraft to provide a 35ft clearance along the net path of the “net-ified” SID.  This allows the operator to treat a SID, which is an all engine operating criteria, as an obstacle clearance criteria and meet 135/91K regulations.

3.    The text accompanying the picture above and the picture below, states that UltraNav maintains 2nd segment, at V2, up to the top of the SID regardless of actual height.  Beyond the limits of the distant obstacle chart, there is no documentation that supports the performance of the aircraft in extended 2^nd segment at these heights above the takeoff surface. This tends to raise the max takeoff weight unrealistically.  The “Net Takeoff Path” is a legal term defined by both the FARS (pt25) and within every AFM.  This Net Takeoff Path is described as a 4 segment path including a level-off / transition / acceleration segment and final / enroute segments. UltraNav does not calculate any of these required segments; rather creating an entirely different path trademarked as “True Flight Path”.  This path, as shown below, does not conform with the AFM and is created by selecting and adjusting 2^nd segment numbers to “average” a path that purportedly will keep the aircraft above the required gradient.  Unfortunately, no aircraft manufacturer endorses this procedure as it extrapolates 2^nd segment data beyond the limits of the 2^nd segment charts and assumes several untested theorems regarding performance degradation.  Lastly, since the path is built upon averaging 2^nd segment values for various altitudes, each of which predicates a specific V2 speed, the resulting path would require an ever changing V2, which is unflyable.  UltraNav acknowledges this dilemma within the text below.

4.    UltraNav reduces the temperature by 2C for each 1000ft height along the 2nd segment path.  The Close In and Distant Obstacle charts already factor temperature, thrust and performance reduction during the 1st, 2nd and transition segments.  UltraNav’s assumption is making the calculation too optimistic.  Conversely, UltraNav does not calculate the Final Segment at all, which does require the temperature reduction.  EFB-Pro allows the pilot to override the 2C reduction for cases of inversion.

5.    The most significant difference between the programs is that UltraNav does not compute transition segment nor max weight final segment (read GREEN optimal flight path below) .  There is no need to “account” for performance degradation per the TFP method.  The AFM contains close-in and distant obstacle charts that adjust for this degradation using ACTUAL flight paths versus the theoretical path ascribed to TFP.  The assumption that the 2^nd segment values degrade with altitude and time (within the 1500ft limit) matches the degradation of 2^nd segment with altitudes beyond 1500 ft is fallacious.  The close-in and distant obstacle charts assume a constant V2 while 2^nd segment values vary with altitude.  Thus a one to one comparison can not be made.  UltraNav responds to this problem by offering a footnote that it reports V2 at the top of the climb, but what speed is required for each 1000 foot increment?  TFM employs mathematical gymnastics which is neither flyable nor aeronautically sound. 

Calculating the geometry of the takeoff profile, including the transition level off segment, is critical in assuring that the aircraft remains above the obstacle gradient during the entire profile. EFB-Pro calculates and reports max weight runway, max weight 2nd segment, transition altitude (in MSL), T/O attitude and max weight final segment.  Note that in the accompanying text from the picture labeled “Actual Screen Shot” above, that UltraNav reduces the climb gradient to 7.3% from 7.6% because of unused runway.  Aside from the fact that UltraNav is attempting to meet the 7.6% gross gradient (addressed in #2 above), this process renders an overly optimistic calculation.  While it is true that the entire runway may not be used, lowering the gradient for this reason implies that more weight can be carried.  If more weight is carried, the transition segment horizontal distance will be longer.  The longer the transition segment distance, in concert with a lower 2^nd segment, places the aircraft at a lower altitude down range and, most likely, below the required climb gradient.  In our repeated calculations, reducing the gradient due to unused runway does not produce a significant max takeoff weight benefit.

To ignore the transition segment and suggest a practice of clearing all obstacles regardless of height in 2^nd segment is a dramatic departure from the AFM.  (see What does the FAA think?)