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ILS Approach in 737-300

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PostPosted: Thu Feb 07, 2008 6:17 am    Post subject: ILS Approach in 737-300 Reply with quote

- For non-EFIS airplanes, before commencing the approach, applicable HSI / NAV switches must be set so that the HSI for the pilots flying indicates ILS navigation signals.

- When operating in speed intervention or an autothrottle SPD mode, timely speed selections minimize thrust lever movement during the approach. This reduces cabin noise levels and increases fuel efficiency. When flaps are extended, select the next lower speed just as the additional configuration drag takes effect. Delaying the speed selection causes an increased in thrust while selecting the lower speed too quickly causes thrust to decrease, then increase.

- APP mode should not be selected until:

1. ILS is tuned and identified
2. Airplane is on an inbound intercept heading
3. Both Localizer and Glide Slope pointers appear on the attitude display properly
4. Approach clearance received

- The glide slope may be captured before the localizer in some airplanes. To avoid unwanted glide slope capture, LOC mode may be selected initially, followed by the APP mode.

- At glide slope capture, observe the flight mode annunciations for correct modes.

- When using the autothrottle to touchdown, no additional wind correction is required to the final approach speed.

- There have been incidents where airplanes have captured false glide slope signals and maintained continuous on glide slope indications as a result of an ILS ground transmitter erroneously left in the ILS Test Mode. False glide slope signals can be detected by checking the final approach fix crossing altitude and VNAV path information before glide slope capture. A normal pitch attitude and descent rate should also be indicated on final approach after glide slope capture. Further, if a glide slope anomaly is suspected, an abnormal altitude range-distance relationship may exist. This can be identified by cross checking distance to the runway with altitude or cross checking the airplane position with waypoints indicated on the navigation display. The altitude should be approximately 300 feet HAT per NM of distance to the runway for a 3 degree glide slope. If a false glide slope capture is suspected, perform a missed approach if visual conditions cannot be maintained.

- For a delayed flap approach (noise abatement) intercept the glide slope with gears down and flaps 15 at flaps 15 speed. The thrust required to descend on the glide slope may be near idle. Approaching 1000 feet AFE, select landing flaps, allow the speed to bleed off to the final approach speed, then adjust thrust to maintain it.

- Flight inspection of ILS facilities do not necessarily include ILS beam performance inside the runway threshold or along the runway unless the ILS is used for Category II or III approaches. For this reason the ILS beam quality may vary and autolands performed from Category I approach at these facilities should be closely monitored. Flight crews must remember that the ILS critical areas are usually not protected when the whether is above 800 foot ceiling and/or 2 mile visibility (in Unites States). As a result ILS beam bends may occur because of vehicle or aircraft interference. Sudden and unexpected flight control movements may occur at a very low altitude or during the landing and rollout when the autopilot attempts to follow the beam bends. At ILS facilities where critical areas are not protected, flight crews should be alert for this possibility and guard the flight controls throughout the automatic approaches and landings. Be prepare to disengage the autopilot and manually land or go-around.

- The “Decision Altitude” value is typically measured by a barometric altimeter and is the determining factor for minima for Category I approaches (e.g. ILS, GLS or RNAV with VNAV). The “Decision Height” value specified in parenthesis, typically a RA height above the touchdown zone (HAT) is advisory. The RA may not reflect actual height above terrain. For most category II and Category III fail passive approaches, the “Decision Height” is the controlling minima and the “Decision Altitude” value specified is advisory. (Fail passive is used instead of Category IIIa to define AFDS certified capability). A decision height is usually based on a specified radio altitude above the terrain on the final approach or touchdown zone.

- Touchdown RVR is normally controlling for Cat I, II and III approaches. For Cat I and II approaches, mid and rollout RVR are normally advisory. For Cat III operations mid and rollout RVR may be controlling. During Cat I approaches, approach lights or other aids should be clearly visible to continue below DA(H). During Cat I and II approaches, descent below 100 feet above touchdown zone elevation requires the red terminating bars or red side row bars (ALSF or Calvert lighting system, or ICAO equivalent , if installed) to be distinctly visible.

If actual touch down RVR is at or above the RVR required for the approach, the runway environment (threshold, threshold lights and markings, touchdown zone, touchdown lights and markings) should become clearly visible resulting in a successful approach. After acquiring the red terminating bars or red side row bars, if the runway environment does not become distinctly visible execute an immediate missed approach. Cat III operations using fail passive autoland systems typically reach a DH of 50 feet when approaching a threshold. In this instance regulations require that the runway environment be clearly visible. If not, execute an immediate missed approach. A review of the approach and runway lighting systems available during the approach briefing is recommended as the pilots has only a few seconds to identify the lights required to continue the approach.
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