EOSID for OEMA - MADINAH / Prince Mohammad Bin Abdulaziz international Airport

OEMA is a regional airport in the western Saudi city of Medina. Opened in 1974, it handles mostly domestic flights, although it has limited scheduled international services to regional destinations such as Cairo, Doha, Dubai, Istanbul andKuwait. and It also handles charter international flights during the Hajj season. It was named after Muhammad bin Abdul-Aziz Al Saud. Only Muslims are allowed to enter the city. This is a strictly enforced law. The Pilgrims for Hajj and Umrah can enter Saudi Arabia through this airport or through Jeddah airport only.

It is the fourth busiest airport in Saudi Arabia, handling 1,592,000 passengers in 2004, including 378,715 Hajj charter passengers. On average, it handles 20-35 flights per day, although this number triples during the Hajj season and school holidays. [www.wikipedia.org]

OEMA has two runways: 17/35 and 18/36 with a mountaineous area on northern side. According to AIP, only runway 35 has a significant obstacle on its takeoff path. It is a mountain with elevation of 2812 ft above sea level.  The Type A - Aerodrome Chart for runway 35 is shown below.

 For the purpose of this analysis we will use an Airbus A330-343 aircraft with MTOW of 233 ton. Considering the above obstacle, the RTOW resulted has an MTOW of 227.3 ton for dry runway condition with takeoff configuration of 1+F, aircon ON, anti-ice OFF, QNH 1013.25 hPa, and wind 0 kt. The 5.7 ton difference is due to an obstacle limitation as shown in the RTOW below.

Thus we need to design an EOSID to avoid this obstacle to increase the MTOW. Since the mountaineous area lies on northern side, we will design an EOSID which turns to the south and ends at ETNAM holding point. The full EOSID procedure text is "Climb STRAIGHT ahead at V2. At D3 PMA turn RIGHT with V2 and max 15 deg bank angle to heading 225 deg. Intercept R-188 PMA outbound to ETNAM and hold as required." The planview of EOSID overlays a contour chart is shown below.

We avoided the obstacle, but now we have 5 new obstacles along the turning takeoff path. It is depicted as red dot on the contour chart. These obstacles have a less gradient (ratio of height to distance) compared to the previous one. The list of new obstacles with its correction height due to turning is given below.

The new RTOW with EOSID successfully increases the MTOW to 240.4 ton. Now, the aircraft can takeoff with full load up to it's operational  MTOW as 233 ton. The final RTOW is shown below.

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VNKT - Kathmandu Airport EOSID Design

Step by steps of EOSID design for this airport with aircraft A320 is as follows:

1. Examine the required data for EOSID: airport/flight procedure data from AIP, terrain data, and aircraft data.

Kathmandu airport is located in the valley surronds by mountanious area. The normal takeoff flight path crossing a high terrain area which requires a very high minimum climb gradient. The terrain and obstacle profile during a takeoff on runway 20 is given in the picture below. 

 

2. MTOW comparison.

The resulted RTOW chart gives MTOW of 59.4 tons for take off with CONF 1+F at 24 deg C OAT as shown below. This MTOW is too low compared to normal MTOW of 77 tons. Thus a EOSID procedure is required to get a higher MTOW.

3. EOSID procedure design.

The EOSID design requires many aspects to be considered. The propossed procedure is climb on runway heading 022 deg to KTM, at D1 KTM RIGHT turn to intercept D4 KTM Arc, crossing R-015 KTM maintain 106 deg magnetic, at D5.7 KTM RIGHT turn to intercept R-106 KTM inbound to KTM, at KTM RIGHT turn to R-015 KTM to intercept D4 KTM Arc, crossing R-084 KTM LEFT turn to intercept R-106 to IGRIS. The pictorial of this procedure and it vertical profile are shown in picture below.

4. Overlay propossed procedure into topographical map.

The 3D view of contour map with the EOSID procedure is shown in picture below.

5. Update obstacles data.

The terrain and obstacles data along the procedure is used to generate a new RTOW chart based on EOSID. The obstacle used with its height correction is shown in table below.

6. New RTOW chart

The new RTOW chart shows a significant increase in MTOW for the same setting as discussed previously. Now it gives MTOW of 68 tons.

7. Re-design EOSID to get a better RTOW chart if your boss is not satisfied.

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EOSID Methods of Analysis

The net takeoff flightpath must clears all obstacles by either 35 feet vertically or 200 feet laterally inside the airport boundary, or 300 feet laterally outside the airport boundary. To operate at the required lateral clearance, the operator must account for factors that could cause a difference between the intended and actual flightpaths and between their corresponding ground tracks. For example, it cannot be assumed that the ground track coincides with the extended runway centerline without considering such factors as wind and available course guidance (reference paragraph 14). This AC will focus on two methods that may be used to identify and ensure clearance of critical obstacles: the Area Analysis Method and Flight Track Analysis Method.

The two methods may be used in conjunction with each other on successive portions of the analysis. For example, an operator may choose to use an area analysis for the initial portion of the takeoff analysis, followed by a flight track analysis, and then another area analysis.

a. The Area Analysis Method defines an obstacle accountability area (OAA) within which all obstacles must be cleared vertically. The OAA is centered on the intended flight track and is Page 6 Par 8 5/5/06 AC 120-91 acceptable for use without accounting for factors that may affect the actual flight track relative to the intended track, such as wind and available course guidance.

b. The Flight Track Analysis Method is an alternative means of defining an OAA based on the navigational capabilities of the aircraft. This methodology requires the operator to evaluate the effect of wind and available course guidance on the actual ground track. While this method is more complicated, it can result in an area smaller than the OAA produced by the Area Analysis Method.

AREA ANALYSIS METHOD.

a. During straight-out departures or when the intended track or airplane heading is within 15 degrees of the extended runway centerline heading, the following criteria apply:

(1) The width of the OAA is 0.0625D feet on each side of the intended track (where D is the distance along the intended flightpath from the end of the runway in feet), except when

limited by the following minimum and maximum widths.

(2) The minimum width of the OAA is 200 feet on each side of the intended track within the airport boundaries, and 300 feet on each side of the intended track outside the airport boundaries.

(3) The maximum width of the OAA is 2,000 feet on each side of the intended track.

b. During departures involving turns of the intended track or when the airplane heading is more than 15 degrees from the extended runway centerline heading, the following criteria apply:

(1) The initial straight segment, if any, has the same width as a straight-out departure.

(2) The width of the OAA at the beginning of the turning segment is the greater of:

(a) 300 feet on each side of the intended track.

(b) The width of the OAA at the end of the initial straight segment, if there is one.

(c) The width of the end of the immediately preceding segment, if there is one, analyzed by the Flight Track Analysis Method.

(3) Thereafter in straight or turning segments, the width of the OAA increases by 0.125D feet on each side of the intended track (where D is the distance along the intended flightpath from the beginning of the first turning segment in feet), except when limited by the following maximum width:

(4) The maximum width of the OAA is 3,000 feet on each side of the intended track.

c. The following apply to all departures analyzed with the Area Analysis Method:

(1) A single intended track may be used for analysis if it is representative of operational procedures. For turning departures, this implies the bank angle is varied to keep a constant turning radius with varying speeds.

(2) Multiple intended tracks may be accommodated in one area analysis by increasing the OAA width accordingly. In a turn, the specified OAA half-widths (i.e., one-half of the OAA maximum width) should be applied to the inside of the minimum turn radius and the outside of the maximum turn radius. An average turn radius may be used to calculate distances along the track.

(3) The distance to an obstacle within the OAA should be measured along the intended track to a point abeam the obstacle.

(4) When an operator uses the Area Analysis Method, the operator does not need to separately account for crosswind, instrument error, or flight technical error within the OAA.

(5) Obstacles prior to the end of the runway need not be accounted for, unless a turn is made prior to the end of the runway.

(6) One or more turns of less than 15 degrees each, with an algebraic sum of not more than a 15 degree change in heading or track, may be analyzed as a straight-out departure.

(7) No accountability is needed for the radius of the turn or gradient loss in the turn for a turn with a 15 degree or less change in heading or track.

FLIGHT TRACK ANALYSIS METHOD.

The Flight Track Analysis Method involves analyzing the ground track of the flightpath. This paragraph discusses factors that the operator must consider in performing a Flight Track Analysis.

a. Pilotage in Turns.

The operator should consider the ability of a pilot to initiate and maintain a desired speed and bank angle in a turn. Assumptions used here should be consistent with pilot training and qualification programs.

b. Winds.

(1) When using the Flight Track Analysis Method while course guidance is not available, operators should take into account winds that may cause the airplane to drift off the intended track.

(2) The operator should take into account the effect of wind on the takeoff flightpath, in addition to making the headwind and tailwind component corrections to the takeoff gross weight used in a straight-out departure.

(3) When assessing the effect of wind on a turn, the wind may be held constant in velocity and direction throughout the analysis unless known local weather phenomena indicate otherwise.

(4) If wind gradient information is available near the airport and flightpath (e.g., wind reports in mountainous areas adjacent to the flightpath), the operator should take that information into account in the development of a procedure.  

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Source: AC No:  120-91  Airport Obstacle Analysis

EOSID Requirements

For aircraft operating above 5700 kg and in accordance with CASA CAO 20.7.1B, operators must comply with paragraph 14 of the order for the development of takeoff performance data and procedures. Sub-paragraph 14.2, states:

“ Procedures to be followed consistent with this Order, including procedures anticipating engine failure at any time between the commencement of take-off and completion of landing, must be specified in the Operator’s Operation Manual. The procedures so specified must be such that they can be consistently executed in service by flight crews of average skill and they must also be such that the take-off flight path with all engines operating is above the one-engine inoperative take-off flight path.”

The takeoff flight path in the context of this guidance and for the purpose of defining the path requirements for an EOSID is as noted below:

The EOSID by definition must commence from a time where engine failure has occurred and where the flight crew are committed to a continued takeoff with one engine out. The takeoff flight path of the EOSID should be able to join a suitable en route path to the planned destination or to another suitable airport or at least have a holding pattern at the end of the EOSID.

The aircraft is considered to be enroute when it is at the higher attitude of 1500 feet:

CAO 20.7.1b Para 12.6

”The net flight path in the en-route configurations must have a positive slope at 1500 feet above the aerodrome where a landing is assumed to be made following engine failure. …”

or the altitude where 1000 feet enroute obstacle occurs

CAO 20.7.1b Para 12.4

“…the en-route obstacle clearance requirements are met if the en-route configuration with a critical engine inoperative the net flight path of an aircraft under V.M.C. clears by 1 000 feet vertically all obstacles within 5 nautical miles of the aeroplane’s track or, under I.M.C., by such greater distance as is determined by the accuracy of the navigation aid(s) used. “

Operationally alternative options are normally considered. This may include climbing to either a minimum safe altitude (MSA), a minimum vectoring altitude (MVA), or a fix and altitude, from which an approach may be initiated to the departure airport or departure alternate. Operators should note that the end of the takeoff flight path is determined by the aircraft’s gross flight path but the obstacle analysis must use the net flight path data.

The takeoff path extends from a standing start to a point, at which the aircraft is at a height of 1500 ft above the takeoff surface, or at which the transition from the takeoff to the en-route configuration is completed and the final takeoff speed is reached, whichever point is higher.

JAR/ FAR 25.111 Takeoff path.

“The takeoff path extends from a standing start to a point in the takeoff at which the airplane is 1,500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and V FTO is reached whichever point is higher.”

CASA accepts the certification of aircraft as detailed in the Aircraft Flight Manual (AFM), however the operational rules of CAO 20.7.1B must be considered in the analysis. If there is any conflict between the AFM data and the operating rules, then if the AFM is more restrictive, that is what must be used. The takeoff path definition assumes that the aircraft is accelerated on the ground to VEF, at which point the critical engine is made inoperative and remains inoperative for the rest of the takeoff. Moreover, the V2 speed must be reached by 35 feet 1 above the takeoff surface (this point is also known as reference zero).

The aircraft must continue at a speed not less than V2 and achieve the regulatory climb and any obstacle clearance requirements until the aircraft reaches the acceleration altitude. The minimum height is 400 feet above the takeoff surface; however operators may select a higher altitude.

This path is a certification requirement and the certification standard is accepted by CASA. The related performance data is contained in the Aircraft Flight Manual (AFM).

Most of the time, runways have surrounding obstacles which should be taken into account prior to takeoff, to ascertain that the aircraft is able to clear them. A vertical margin has to be considered between the aircraft and each obstacle in the takeoff flight path. This margin, based on a climb gradient reduction, leads to the definitions of the Gross Takeoff Flight Path and the Net takeoff flight Path.

Gross Flight Path = Takeoff flight path actually flown by the aircraft, based upon the gross height attained. The flight path commences at reference zero.

Net Flight Path = Gross takeoff flight path minus a mandatory reduction, based upon the net height attained.

The gradient reduction is considered to account for pilot technique, degraded aircraft performance, and ambient conditions. The net takeoff flight path data must be determined so that they represent the actual (Gross) takeoff flight path reduced at each point by a gradient equal to:

0.8% for two-engine aircraft

0.9% for three-engine aircraft

1.0% for four-engine aircraft

CAO 20.7.1B Para 7.5

“In determining the net flight path of an aeroplane to show compliance with subsection 12, the gross gradients of climb achieved in paragraphs 7.2 and 7.4 must be reduced by 0.8% for twin-engined aeroplanes, 0.9% for three-engined aeroplanes and 1.0% for four-engined aeroplanes.”

The takeoff flight path can be divided into several segments. Each segment is characteristic of a distinct change in configuration, thrust, and speed. Moreover, the configuration, weight, and thrust of the aircraft must correspond to the most critical condition prevailing in the segment. Finally, the flight path must be based on the aircraft’s performance without ground effect. As a general rule, the aircraft is considered to be out of the ground effect, when it reaches a height equal to its wing span.

After an engine failure at VEF, whatever the operational conditions, the aircraft must fulfill minimum climb gradients, as required by the aircraft flight manual and the operational requirements of CAO 20.7.1B.

Figure above, summarizes the different requirements and aircraft configuration during the four takeoff segments. This includes the minimum required climb gradient with an engine out, flaps / slats configuration, engine power rating, speed reference, and landing gear configuration.

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Source:

CAAP 235-4(0): Engine Out SID (EOSID) and Engine Out Missed Approach Procedures

Introduction to EOSID

Engine out takeoff guidance has a number of names as adopted by industry, some of the common names include:

1. Engine Out Departure Procedures

2. Engine Out Contingency Procedures

3. Engine Out Escape Paths

4. Engine Out SIDs

The name selected is optional but it must reflect the approved kind of operation of the aircraft. Items 1, 2 and 3 can make reference to both VMC and IMC operations and must have the appropriate guidance for the operation type. Item 4, as the name suggests is based on IMC operations. Although not a requirement of CAO 20.7.1B, the majority of the aircraft that operate to this CAO are IFR approved. For IFR approved aircraft an EOSID must cover takeoffs in both VMC and IMC. From this point forward engine out takeoff guidance will be referred to as an EOSID.

Standard Instrument Departures (SIDs) or departure procedures (DPs) are designed in accordance with U.S. Standards for Terminal Instrument Procedures (TERPS) or ICAO Pans-Ops. These are based on normal all-engine operations and assume that the aircraft are capable of maintaining a climb profile. These departure procedures are normally published as specific routes to be followed or as omni-directional departures, together with procedure design gradients and details of significant obstacles. They are normally established for each runway where instrument departures are expected to be used and they define a departure procedure for the various categories of aircraft used.

In the event of an engine failure, continued adherence to departure procedures may not be possible as SIDs or DPs do not necessarily assure that engine-out obstacle clearance requirements are met. An engine failure during takeoff is a non-normal condition, and therefore, takes precedence over noise abatement, air traffic, SID’s, DPs, and other normal operating considerations. The fundamental difference between SIDs and EOSIDs is that SIDs provides the minimum performance considerations to meet the departure requirements assuming an all engine operation whereas EOSIDs are based upon engine out performance in relation to obstacle clearance. EOSIDs can be in the form of a straight departure and or a series of turns.

Note: Development of Engine Out Takeoff Procedures is the responsibility of the operator.

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Source:

CAAP 235-4(0): Engine Out SID (EOSID) and Engine Out Missed Approach Procedures