In A Look at the Descent Leg, we discussed some of the steps pilots take upon vacating cruise altitude. With this post, we’ll go into more detail about the final portion of the descent segment: the approach and landing. As you probably know, this final segment is one of the most vital of the entire flight and requires the crew’s full attention. Let’s examine some of these duties your crewmembers perform.
The airspeeds used by airliners vary depending on temperature and aircraft weight. Prior to commencing the approach, pilots will calculate three (sometimes more) relevant speeds. The first, referred to as approach speed, is the speed flown during the latter stages of the final approach to just short of the runway threshold. This relatively slow speed permits a stabilized approach with the aircraft fully configured (landing gear and flaps extended). At times, approach speed will be adjusted for strong, gusty winds or when other than normal flap settings are used.
The second common speed, VYSE, provides the best climb rate with an engine inoperative. While engine failure during approach is extremely rare, flight crews always prepare for the worst-case scenario. Should a powerplant failure require an aborted landing, the crew is prepared with the requisite climbout speed.
VREF, the lowest of the three speeds, is the target airspeed when crossing the runway threshold. Once the aircraft is fully configured and the landing is assured, pilots will reduce power to achieve VREF. This speed is desirable because it reduces landing distance and stress on the landing gear & tires, and yet still maintains a safe margin above stalling speed. All three speeds are calculated and marked with speed bugs, which facilitate easy identification by the crew.
Configuring the Airplane
An important prerequisite for landing is to ensure the landing gear is extended and locked into position. How do the pilots know when to do this? Gear extension, flap deployment, and all other necessary tasks are specifically outlined in the landing approach profile. Your pilots will ALWAYS refer to checklists to verify these steps are completed correctly, but it’s a good bet most pilots also have these procedures memorized.
The landing gear and flaps also have their own V speeds, which indicate the maximum velocity they may be operated and/or remain in the extended position. During approach, pilots will slow the aircraft below these V speeds and deploy landing gear and flaps incrementally. You’ve probably seen the flaps extend during the approach, as well as heard a “clunk” as the landing gear locked into place. Rest assured, these extensions are far from arbitrary and are specifically spelled out for all conceivable types of approaches.
What happens if the gear fails to extend? While this possibility is rare, the aircraft manufacturers have built in numerous safeguards and backup extension plans. Your pilots have also trained ad nauseam to handle such problems. If, worst-case scenario, the gear still fails to extend, a safe landing is still probable. Usually, the crew will inform airport personnel to “foam the runway,” which reduces friction/sparks and the chance of fire. In addition, it’s a sure bet they’ll have fire trucks and ambulances standing by. When a belly landing is necessary, such an event is almost never fatal and any injuries received are usually minor.
Airplanes normally descend at a 3 degree angle and receive guidance from both electronic and visual aids. At most commercial airports, airliners will fly an ILS (instrument landing system) approach, which gives lateral and vertical guidance. Though designed for instrument weather, nearly all crews still utilize this approach system in visual conditions. In many cases, they’ll let the autopilot fly most (sometimes all) of the approach. Next to the runways, external light systems also provide information on the aircraft’s approach angle to aid crews if adjustments are necessary. The combination of these systems can guide aircraft virtually to the pavement.
While the approach segment can be a nervous time for some passengers, the pilots have been thoroughly trained in every possible aspect of this phase. If something unexpected does occur, your crew is adequately prepared to handle the event. On your future flights, rest easy knowing you’re in the safe hands of an experienced crew.