Safety Features - Landing Gear - Airframes & Aircraft Systems #18

Summary

This lesson focuses on the critical safety features of aircraft landing gear systems, ensuring correct operation and preventing damage. It covers the mechanisms for nosewheel alignment, gear retraction safety devices, and gear extension warnings. The script also discusses ground locks, emergency lowering systems, and the pilot's responsibility for aircraft configuration. The lesson highlights the importance of these systems in maintaining flight safety.

Takeaways

• 🔐 Safety features in aircraft landing gear systems are crucial for preventing damage and ensuring correct operation.
• 🎯 The nosewheel must be aligned in the fore and aft direction before retraction, which is achieved through hydraulic centering or self-centering cams.
• 🚫 A mechanical lock with an electrically operated solenoid prevents the landing gear from being retracted unsafely.
• ⚙️ On smaller aircraft, the solenoid is controlled by switches on the main gear shock absorber struts, which close as the struts extend.
• 🔄 Larger aircraft require additional criteria, such as correct gear truck angle and body gear steering alignment, before the gear can be safely retracted.
• 🔄 An override mechanism is provided for maintenance and in case of solenoid failure, but should be used with caution to avoid damage.
• 🔒 Landing gear ground locks or locking pins prevent the gear from retracting when the aircraft is on the ground, ensuring safety.
• 🚨 An aural warning system alerts pilots if the landing gear is not locked down, with an isolation switch for specific flight exercises.
• 🛠️ In the event of a hydraulic system failure, there are provisions to manually lower and lock the landing gear in the down position.
• ✈️ The pilot remains ultimately responsible for ensuring the aircraft's correct configuration for each phase of flight, despite the presence of safety systems.

Q & A

Why is the correct operation of the landing gear considered of utmost importance?

The correct operation of the landing gear is of utmost importance because it ensures the safety of the aircraft and its occupants during takeoff and landing.

What are the safety features included in the retraction and extension systems of the landing gear?

The safety features in the retraction and extension systems include mechanisms to stop the gear from retracting when it's not safe, warnings to the crew if they attempt to land with the gear not extended, and methods to ensure the nosewheel is aligned before retraction.

How does the hydraulic nose wheel centering method work on aircraft with powered steering?

On aircraft with powered steering, the hydraulic nose wheel centering method automatically aligns the nosewheel in the fore and aft direction prior to retraction.

What is the purpose of the mechanical lock in the landing gear selector lever?

The mechanical lock in the landing gear selector lever prevents the gear from being retracted when it's not safe to do so by retaining the selector in the down position until released by an electrically operated solenoid.

How do the switches on the main gear shock absorber struts control the electrical power to the solenoid in smaller aircraft?

In smaller aircraft, the switches on the main gear shock absorber struts control the electrical power to the solenoid by being open when the struts are compressed and closing as the struts extend after takeoff, thus releasing the selector lever lock.

What additional criteria must be met on larger aircraft before it is safe to raise the landing gear?

On larger aircraft, additional criteria such as the main gear trucks being tilted to the correct angle and the gear being aligned for aft-only movement must be met before the lever lock is released to raise the landing gear.

What is the purpose of the landing gear ground locks or locking pins?

Landing gear ground locks or locking pins are safety features designed to prevent the inadvertent retraction of the gear when the aircraft is on the ground, ensuring that the gear cannot move while they are in position.

How does the aural warning system work in the landing gear system?

The aural warning system in the landing gear provides an audible alert if the gear is not locked down, typically triggered by certain combinations of flap and throttle positions, and can be silenced using an isolation switch except in critical conditions.

What is the Enhanced Ground Proximity Warning System (EGPWS) and how does it relate to the landing gear?

The Enhanced Ground Proximity Warning System (EGPWS) provides a 'too low gear' warning if the aircraft passes a specified radio altitude with the gear not locked down, supplementing the safety measures for landing gear operation.

How can the landing gear be lowered in the event of a hydraulic system failure?

In the event of a hydraulic system failure, the landing gear can be lowered using alternative methods such as electrically releasing the up locks, using a hand pump, or activating an emergency pressure system that may utilize hydraulic accumulators or pneumatic storage cylinders.

What is the responsibility of the pilot regarding the landing gear configuration?

The pilot is ultimately responsible for ensuring that the aircraft is in the correct configuration for each phase of flight, which includes verifying the landing gear is properly extended or retracted as required.

Outlines

00:00

🛫 Landing Gear Safety Features

This paragraph discusses the critical safety features of aircraft landing gear systems, which are designed to ensure correct operation under all conditions. It highlights the importance of nosewheel alignment during retraction and the various methods used to achieve this, including hydraulic nose wheel centering and self-centering cams. The paragraph also explains safety devices that prevent the landing gear from being retracted unsafely, such as mechanical locks and electrically operated solenoids. Additionally, it covers the process on smaller and larger aircraft, the use of ground locks or pins to prevent inadvertent retraction, and the aural warning system that alerts pilots if the gear is not locked down during flight.

05:02

🔐 Landing Gear Emergency Procedures

The second paragraph focuses on the emergency procedures for landing gear operation. It details how the landing gear can be manually lowered and locked in the down position in case of a hydraulic system failure. The paragraph outlines the different mechanisms used in modern aircraft, such as electrically operated motors in the Boeing 747 and mechanical cables in the Boeing 737. It also mentions the absence of power to close the hydraulic doors after manual extension, leading to the illumination of the door open light. Furthermore, it discusses the emergency pressure systems that can extend the landing gear, which may be powered by hydraulic accumulators, hand pumps, or pneumatic storage cylinders. The paragraph concludes with a reminder that pilots are ultimately responsible for ensuring the aircraft's correct configuration for each phase of flight.

Keywords

💡Landing Gear

The landing gear refers to the undercarriage of an aircraft that is used for takeoff and landing. In the video, the correct operation of the landing gear is emphasized as crucial, with multiple safety features incorporated to ensure it functions properly under all conditions. The landing gear system includes mechanisms to prevent retraction when it's unsafe and to warn the crew if the gear is not extended during landing.

💡Safety Features

Safety features are critical components designed to ensure the proper functioning of the landing gear. These include devices to prevent inadvertent retraction on the ground and warnings to alert the crew if the landing gear is not extended. The video discusses various safety features, such as mechanical locks, solenoids, and warning systems, that work together to prevent accidents during takeoff and landing.

💡Nosewheel Centering

Nosewheel centering ensures that the nosewheel is aligned in the fore and aft direction before retraction to avoid damage to the airframe. The video describes methods like hydraulic nose wheel centering and self-centering cams that automatically align the nosewheel during takeoff, highlighting the importance of proper alignment for the safe retraction of the landing gear.

💡Solenoid

A solenoid is an electrically operated device used to control the mechanical lock that prevents the landing gear from being retracted when it's not safe. In smaller aircraft, the solenoid's electrical power is controlled by switches on the main gear shock absorbers. The video explains how the solenoid plays a critical role in releasing the selector lever lock to allow the gear to be retracted only when it is safe to do so.

💡Landing Gear Selector Lever

The landing gear selector lever is a control in the cockpit that allows the pilot to raise or lower the landing gear. The video explains that this lever is mechanically locked in the down position to prevent inadvertent retraction and can only be released when certain safety criteria are met, such as the extension of shock absorber struts after takeoff.

💡Ground Locks

Ground locks, also known as locking pins, are safety devices that prevent the landing gear from retracting while the aircraft is on the ground. These pins or metal sleeves are inserted into the landing gear mechanism, making it impossible to move the gear. The video mentions that ground locks are equipped with warning flags to prevent the crew from taking off with them still in place.

💡Aural Warning

An aural warning is an audible alert system that notifies the crew if the landing gear is not locked down during critical phases of flight, such as landing. The video discusses how different aircraft use various criteria, such as flap and throttle positions, to trigger this warning, ensuring that the landing gear is properly extended before landing.

💡Free Fall Method

The free fall method is a backup procedure used to lower the landing gear in the event of a hydraulic system failure. The video describes how the landing gear can be manually released from its up locks and allowed to drop into the down position under its own weight. This method ensures that the gear can still be deployed even if the primary system fails.

💡Emergency Pressure System

The emergency pressure system is an alternative method for extending the landing gear in case of a failure in the normal hydraulic system. The video explains that this system may use various sources of pressure, such as a hydraulic accumulator or a hand pump, to ensure the landing gear can be safely lowered and locked in place during an emergency.

💡EGPWS (Enhanced Ground Proximity Warning System)

EGPWS is a safety system designed to prevent controlled flight into terrain by providing alerts if the aircraft is too low with the gear not extended. The video briefly mentions that EGPWS will give a 'too low gear' warning if the aircraft descends below a certain altitude without the landing gear being locked down, enhancing overall flight safety.

Highlights

The importance of landing gear's correct operation is emphasized with numerous safety features.

Safety features prevent gear retraction when unsafe and warn the crew if attempting to land with gear not extended.

Nosewheel must be aligned fore and aft before retraction, achieved through hydraulic centering or self-centering cams.

A mechanical lock with an electrically operated solenoid prevents the landing gear selector from being moved up unsafely.

On smaller aircraft, electrical power to the solenoid is controlled by switches on the main gear shock absorber struts.

Larger aircraft require additional criteria like correct gear truck angle and body gear steering alignment before gear can be raised.

An override mechanism is provided for solenoid failure and maintenance, but should be used with caution.

Landing gear ground locks or locking pins prevent inadvertent retraction when on the ground.

Ground locks are fitted with warning flags to prevent the crew from getting airborne with them still in position.

An aural warning system alerts pilots if the gear is not locked down, with an isolation switch for certain flight exercises.

The EGPWS provides a 'too low gear' warning if passing a specified radio altitude with the gear not locked down.

A means of manually lowering the landing gear is provided for hydraulic system failures.

In modern aircraft, up locks may be released electrically or mechanically, allowing the gear to drop under its own weight.

If the gear is lowered manually, the hydraulic doors may remain open, and the door open light will stay illuminated.

Some aircraft have an emergency pressure system for extending the landing gear, using alternative pipelines or storage devices.

Pilots are ultimately responsible for ensuring the aircraft's correct configuration for each phase of flight.

Transcripts

since the correct operation of the

landing gear is of the utmost importance

a number of safety features are included

in the retraction and extension systems

to ensure its correct operation under

all conditions

safety features are also built-in to

stop the gear being retracted when it's

not safe to do so

and to warn the crew if they are

attempting to land with the gear not

extended

in this lesson we will discuss these

safety features

to avoid damage to the airframe

structure the nosewheel must always be

aligned in the fore and aft direction

prior to retraction

a number of methods are used to ensure

that this happens automatically

one method already discussed is

hydraulic nose wheel centering on

aircraft with powered steering

other systems use a self centering cam

which will move the nose wheel into the

correct position as the olio pneumatic

strut extends on takeoff

to prevent inadvertent

of the landing gear when it's not safe

to do so the safety device is

incorporated which prevents the landing

gear selector lever being selected up

this safety device consists of a

mechanical lock which retains the

selector in the down position and is

released by the operation of an

electrically operated solenoid

on smaller aircraft electrical power to

the solenoid is controlled by switches

mounted on the main gear shock absorber

struts

when the struts are compressed the

switches are open but as the struts

extend after takeoff the switch contacts

close and the electrical supply to the

solenoid is completed thus releasing the

selector lever lock and allowing the

landing gear to be selected up

[Music]

larger aircraft a number of additional

criteria have to be met before it is

safe to raise the gear for instance the

main gear trucks may have to be tilted

to the correct angle and for the

aircraft with body gear steering the

gear will have to be aligned for an aft

only then will the lever lock be

released

a means of overriding the lock such as a

separate gated switch to complete the

circuit or a mechanical means of

releasing the lock is provided for use

in the event of solenoid failure and for

maintenance purposes

flight crews should exercise great care

in using this bypass facility normally

it should only be used when called for

in a checklist as raising the gear

hydraulically when parts of it are

incorrectly positioned can cause

catastrophic damage to both the gear and

the airframe

landing gear ground locks or locking

pins our further safety features which

are intended to prevent inadvertent

retraction of the gear when the aircraft

is on the ground

they will usually consist of pins or

metal sleeves which interfere with the

operation of the gear in such a way that

it is impossible for the gear to move

when they are in position

they are fitted with warning flags which

help prevent the crew from inadvertently

getting airborne with them still in

position on the gear

if they are still fitted when the crew

do their external inspection a further

external check should be carried out

after they've been removed as getting

airborne with them fitted will often

require the dumping of fuel before

landing again to have them removed

on some aircraft after removal they are

stowed onboard in a position visible to

the crew

guard against landing with the landing

gear not locked down an aural warning is

incorporated in the system

an aural warning isolation switch is

often provided to allow certain flight

exercises to be carried out without

unnecessary warnings

different aircraft types use different

criteria for the operation of the oral

warning and isolation switch these

normally involve a combination of flap

and throttle positions

in a typical system if the flaps are at

an intermediate position with the gear

not locked down

or the throttles are the

warning will sound

the isolation switch can be used to

silence the warning

if however landing flap is selected with

the gear not locked down then again the

warning will sound

but operation of the isolation switch

will not silence it

if fitted the enhanced ground proximity

warning system EGPWS will give a to low

gear warning passing a specified radio

altitude with the gear not locked down

eg PWS is covered fully in this series

of lessons on aircraft instruments

a means of lowering the landing gear and

locking it in the down position is

provided to cater for the possibility of

failure in the normal system

in most modern aircraft the up locks may

be released electrically as in the case

of the Boeing 747 where the switches

control electric motors which operate up

blocks

or mechanically as in the case of the

Boeing 737 where the handles in the

cockpit are connected by cables to the

up block release mechanisms

in both of these cases once the up locks

have been released the landing gear

lowers or free falls under its own

weight and the down locks are engaged

mechanically by Springs

in the typical system depicted here

pulling the handle to the first detent

releases the door up lock allowing the

door to fall open

the second detent releases the gear up

lock which allows the gear to drop to

the down position

a heavy spring in the down lock actuator

forces the over center mechanism into

the locked down position

if the gear has been lowered by this

freeform method there will be no power

available to close the hydraulically

operated doors after extension so they

will remain open and the door open light

will remain illuminated

on some aircraft the landing gear can be

extended by an emergency pressure system

which may use alternative pipelines to

the jacks

sure for the emergency system may be

supplied by a hydraulic accumulator a

hand pump an electrically powered pump

or even a pneumatic storage cylinder

that is the end of the lesson

you should now know how the landing gear

can be lowered in the event of a

hydraulic system failure

you should be familiar with the methods

used for preventing the landing gear

retraction on the ground

and for preventing a landing being made

with the gear up remember however that

these systems are not foolproof the

pilot is ultimately responsible for

ensuring that the aircraft is in the

correct configuration for the face of

flight