TCAS (Traffic Collision Avoidance System)

Traffic Collision Avoidance System

TCAS and IVSI Indicator

The Traffic alert and Collision Avoidance System (or TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision (MAC). It is an implementation of the Airborne Collision Avoidance System mandated by International Civil Aviation Organization to be fitted to all aircraft with MTOM (maximum take-off mass) over 5700 kg or authorised to carry more than 19 passengers.

Official definition from PANS-ATM (Nov 2007): ACAS / TCAS is an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders.

In modern glass cockpit aircraft, the TCAS display may be integrated in the Navigation Display (ND); in older glass cockpit aircraft and those with mechanical instrumentation, such an integrated TCAS display may replace the mechanical Instantaneous Vertical Speed Indicator (which indicates the rate with which the aircraft is descending or climbing).

Read more : http://en.wikipedia.org/wiki/TCAS

FMC (Flight Management Computer)

Introduction

First introduced on the series 200 in Feb 1979 as the Performance Data Computer System (PDCS), the Flight Management Computer (FMC) was a huge technological step forward. Smiths Industries (formerly Lear Seigler) has supplied all FMCs installed on the 737.

The PDCS was developed jointly by Boeing and Lear Seigler in the late 1970's. It enabled EPR and ASI bugs to be set by the computer and advise on the optimum flight level, all for best fuel economy. It was trialed on two in-service aircraft, a Continental 727-200 and a Lufthansa 737-200 for nine months in 1978 with regular line crews and a flight data observer. The 737-200 showed average fuel savings of 2.95% with a 2 minute increase in trip time over an average 71 minute flight. The 727 gave a 3.94% fuel saving because of its longer sector lengths. The PDCS quickly became standard fit and many were also retrofitted. By 1982 the autothrottle had been devised and thrust levers could be automatically driven to the values specified by the PDCS.

The true FMC was introduced with the 737-300 in 1984 this kept the performance database and functions but also added a navigation database which interacts with the autopilot & flight director, autothrottle and IRSs. The integrated system is known as the Flight Management System (FMS) of which the FMC is just one component. Most aircraft have just one FMC, but there is an option to have two this is usually only taken by operators into MNPS airspace eg Oceanic areas. The FMS can be defined as being capable of four dimensional area navigation (latitude, longitude, altitude & time) while optimising performance to achieve the most economical flight possible.

The photograph above is of the Control Display Unit (CDU), which is the pilot interface to the FMC. There are normally 2 CDUs but only one FMC. Think of it as having two keyboards connected to the one PC. The CDU in the photograph has a DIR INTC key at the beginning of the second row but some have a MENU key. This key gives access to the subsystems such as FMC, ACARS, DFDMU, etc.

In its most basic form, the FMC has a 96k word navigation database, where one word is two bytes (ie a 16 bit processor). This was increased to 192k words in 1988, 288k in 1990, 1 million in 1992 and is now at 4 Mega words for the 737-NG with Update 10.7. The navigation database is used to store route information which the autopilot will fly when in LNAV mode. When given data such as ZFW & MACTOW, it takes inputs from the fuel summation unit to give a gross weight and best speeds for climb, cruise, descent, holding, approach, driftdown etc. These speeds can all be flown directly by the autopilot & autothrottle in VNAV mode. It will also compute the aircrafts position based upon inputs from the IRSs, GPS and radio position updating.

The latest FMC – Model 2907C1, has a Motorola 68040 processor running at 60MHz (30Mhz bus clock speed), with 4Mb static RAM and 32Mb for program & database.

Read more : http://www.b737.org.uk/fmc.htm

ILS approaches

What does "ILS" stand for?

Instrument Landing System.

What is an ILS?

In a nutshell, it is an instrument approach that gives the pilot of an aircraft visual cues on the aircraft's instruments. If the pilot follows these cues he will arrive near the approach end of the runway, usually 200 feet above the surface.

How does the ILS differ from the other types of approaches?

Generally speaking, it is the most accurate of the approaches that is available to the average civilian pilot, and allows you to descend to lower minimums. The word "minimums" refers to height (above the ground), and visibility.

The ILS offers both horizontal and vertical guidance information, whereas the VOR and NDB approaches offer horizontal (lateral) guidance only. Because it offers vertical guidance, the ILS is in the category of a "Precision Approach".

What equipment do I need in my airplane to fly the ILS?

You will need a VOR head, with glideslope display, or an HSI (Horizontal Situation Indicator). "Glass cockpits" replace these instruments with a variety of displays on CRT's (Cathode Ray Tubes). Because of the variety of displays, glass cockpits will not be referenced in this tutorial. However, the procedures remain the same. In addition, you will need a Marker Beacon receiver to indicate passage over the ground components of the ILS. An ADF or RMI, while extremely handy for orientation, is not required.

OK. what surface equipment "makes" an ILS?

1. Localizer: This is the component that provides the "left/right" guidance. Think of it as the VOR needle if you will, just more sensitive.

2. Glide Slope: This is the component that provides the "up/down" guidance. Think of it as a VOR needle laying on it's side. And, like the Localizer, it is more sensitive than the VOR display.

3. Outer Marker: This guy is in line with the Localizer's extended center line across the ground. It is normally located four to seven miles from the threshold of the runway. It transmits a signal on 75 MHz with a 400 Hz tone timed at two dashes per second. In addition to this audio tone, a blue light on the Matker Beacon receiver will flash in rhythm with the audio tone.

4. Middle Marker: Like the Outer Marker, located on an extended center line from the runway. It is normally located at the Decision Height (Missed Approach Point), on the approach, usually .5 to .8 miles from the runway threshold.

5. Approach Lights: These are the guys that John Wayne saw when he broke out on the approach into San Francisco in the movie "The High and The Mighty", along to the strains of a large orchestra. They are designed to help the pilot transition from the cockpit displays to outside visual reference for the landing. There are a various ways these are displayed. Each type has a designation, such as "ALSF-1", "ALSF-2", "SSALR", "MALSR", and so on. Suffice it to say that the "approach lights" that you see on the approach are approved by the appropriate governing authorities to do the job.

Just a second here. How do you "tune" the Marker Beacons? I don't see any radios for that purpose

Well, you can't tune them- so there! Here's the deal. All Marker Beacons transmit on the same frequency, 75 MHz. The Outer and the Middle Beacons differ in the audio tone that they emit. The Marker Beacon receiver in the aircraft is tuned to this set frequency, you as the pilot can't do any more about it. You can turn the audio off, and on some receivers you can adjust the "sensitivity" from "low" to "high". The lights associated with the Outer and Middle Markers will flash automatically. So, why aren't you bombarded with these "whistles and bells" as you fly across the country? Because they are low-powered, and once you are several thousand feet above the ground the Marker Beacon receiver will not capture the signals.

Read more : http://stoenworks.com/Tutorials/ILS Approaches.html