Check out our Facebook page where you'll find the example figures talked about in this episode.

For more information, here are some references 

FCOM DSC-22_30-90 SPEED mode in approach phase

FCOM PRO-SUP-10 OTHER SPEEDS

FCTM NO-110

• 29 March 2015
• A320 Toronto - Halifax
• Winter time, forecast in Halifax wind 15kts G25 with moderate drifting snow and a temp of -5 and vis 1/2sm (800m).
• In cruise, received METAR 1/4sm vis (400m) with heavy snow
  NOTAMED that Glide path U/S so they set up for a LOC only.
• Calculated cold temp correction for FAF alt, MDA and GA alt.
• Calculated FAF to be 2200ft ASL (+200ft correction)
  MDA they added 23ft for temp and 50ft for the company
• see FCTM - SI -010 (approach)
• Using their company qrh converter the adjusted the FPA from 3.1 to 3.5°
• In level flight before reaching the FAF they pulled FPA and selected 0
  0.3nm before FAF they selected fpa -3.5
• As the a/c descended it diverged from the desired profile due to wind variations. This divergences continued throughout the approach.
• A 400’ auto call out was made as they descended through MDA 1.2nm from threshold
• PM called “minimum, lights only” as per their SOP. The aircraft was 1nm from the threshold now.
• PF saw the approach lights and called landing
• At MDA the aircraft was 0.3nm further back than published
• At 0.7nm from threshold crew confirmed visual with the approach lights. The reports says they were over a lighted facility.
• AP was disconnected just above 100' RA
• At the 50ft auto callout the PM called "pull up"
• The aircraft struck and severed a power line that was perpendicular to the runway causing power outage to the terminal
• TOGA was selected about 1 second before ground impact and a full, pull up, demand was made on the side stick.
• The left landing gear struck an approach light about 860ft before the threshold. Then the main landing gear, aft fuselage and the left engine hit the snow covered ground, bounced, took out the LOC antenna, bouncing twice more before skidding along the runway, coming to rest about 1900ft after the threshold.
• Power to the aircraft was lost during the ground contacts leaving only the emergency lights on in the cabin.
• Pax were evacuated successfully with no deaths. 1 cabin crew member was seriously injured and the were 25 minor injuries.
• The flight crew were pretty experienced with the Captain having over 5700 hours and the FO 6300 hours on type.
• Errors/factors
  The Auto pilot limitation on a NPA is AT MDA. AP was actually disconnected 23 seconds after passing MDA
  Didn't monitor DIST/ALT table on chart. "At Air Canada, the use of dist/alt table on jepp charts as a monitoring tool is not cited during pilot training fro loc/npas
  CT (canadian CAA/FAA) didnt raise this as an issue at any inspections.
  This is critical because of the limitations of the FPA

• According to the report, Air Canada pilots didnt have access to the FCOM, only the company manuals.
  FCOM doesnt offer any guidance on how to adjust the FPA e.g how much for how long.
• For your info, 0.1º change will affect the a/c path by 10ft over the next NM so for example if youre on a 3º glide and youre 30ft high at a height check, increasing the FPA to will get you back on profile in 1 NM. so 0.1º per 10ft. just remember to reset to 3º once its back on profile!
• Contrary to this, "air canada's practice was the, once the a/c was past the FAF, flight crews were not required to monitor the a/c's alt and dist from the threshold, nor make any adjustments to the FPA. Also, Airbus said at the time that before the FAF press TRK/FPA pb, select desired FPA on the FPA dial and then at 0.3 before the FAF - pull. Air canadas practice was to pull v/s/FPA selecting 0 and then wind it to desired angle at FPA -0.3
• Unlike EASA and FAA, in canade the minimum vis for an approach isnt afected by the type of ALS installed. As a comparison, for the minima at halifax the FAA would require an additional 900m of approach lighting!!

You can read the report yourself by clicking on this link:

http://www.bst-tsb.gc.ca/eng/rapports-reports/aviation/2015/a15h0002/a15h0002.asp

Matt & Andy carry on where they left off. Last week they talked about the 7 main factors affecting approach and landing accidents. As a reminder they covered,

• SOPs 
• Crew cooperation (CRM)

In this episode they discuss,

• Altimeter and altitude issues
• Descent and approach management 
• Approach hazard awareness
• Readiness to go around 
• Approach and landing techniques

75 % of approach-and-landing incidents and accidents come under 5 categories:

• CFIT (which includes landing short of runway); 

• Loss of control; 

• Runway overrun; 

• Runway excursion; and, 

• Non-stabilized approaches. 

They looked at the factors that often lead to these accidents. They broke them down into 7 different subjects,

SOPs 

Crew cooperation (CRM)

Altimeter and altitude issues

Descent and approach management 

Approach hazard awareness

Readiness to go around 

Approach and landing techniques

Listen to episodes 15 & 21 for a refresher on the CRM topics discussed in this episode.

The Ground Proximity Warning System (GPWS) generates aural and visual warnings, when one of the following conditions occurs between radio heights 30 ft and 2 450 ft

Mode 1: Excessive rate of descent

Mode 2: Excessive terrain closure rate

Mode 4: Unsafe terrain clearance when not in landing configuration

Mode 5: Too far below glideslope.

A Terrain Awareness Display (TAD), which predicts the terrain conflict, and displays the terrain on the ND.

A Terrain Clearance Floor (TCF), which improves the low terrain warning during landing.

On newer aircraft the GPWS occurs between radio heights 10 ft and 2 450 ft.

For more info see FCOM DSC-SURV-040

This week Matt and Andy look at a scenario where 2 fuel pumps in the same wing are lost

This week Matt and Andy take a look at the slat flap jammed checklist and look through the flap system

Here are the pertinent points from Matt's information;

1. No oil quantity indications after the FADECs have depowered. You need to power them manually using the guarded switches on the maintenance panel.

2. Engine start with anything but cold engines take a long time. 

3. Single Pack operation causes the engines to increase thrust significantly and can cause high brake temperatures

4. Warm up and cool down times are very important - 3 min warm up and cool down unless cold engine which requires 5 min warm up.

5. Significant sound difference

This Week Matt and Andy look in to the unreliable speed checklist as requested by one of our listeners. 

It is probably worth going back and listening to episode 6 where we discussed the systems involved in a bit more detail.

This week Matt & Andy look at the new (for some) Emergency Evacuation procedure. Remember that these procedures will still vary slightly from airline to airline so it's important to check your manuals to make sure you're doing them correctly.

This week Matt discusses how Airbus are changing the way the manuals are organised. 

It's the NEO Trio (see what we did there!)

Engine starting.
This is the most common thing we do with them so seems like a good place to start.
The sequence is still the same but helpfully, Airbus have decided to change the names of the controls, so, the ENG MASTER switch’ is now called ‘ENG MASTER lever’
And the ‘ENG MODE selector’ is now called ‘ENG START selector’

So as you do with the CEO, you turn the ENG START selector to IGN/START and this brings up the engine system page and closes off the pack valve.

When the engine master Lever is set to 'on' the start sequence begins.

On the CEO, the sequence runs like this,
The LP fuel valve opens
Start valve is opened
APU speed is increased (if that's being used for start)
If starting in the ground, When N2> 16% ignitions starts. In the air it's immediate
On the ground, when N2> 22% the HP Fuel valve opens. In flight it's when N2> 15%
Once the N2 gets above 50% the start valve closes, the igniter goes off unless in the air, the APU speed reduces to normal speed and the pack valve remains closed for 30 seconds (which you will already know of course because we discussed that a few months ago in our air conditioning episode!)
So what does the LEAP engine do?
Well for a start (no pun intended), the FADEC will initiate ignition and fuel flow at an optimal point during the start process instead of at defined N2 values like the CEO.
The numbers stated in the FCOM are pretty much the same, >15% N2 for ignition start (immediately if airborne) and >20% N2 for the HP fuel valve to open both on the ground and in the air.

As you can see, the procedure is the same, turn the engine start selector to ignition and then move the desired engine master lever to on.

Now, after starting, we normally do the approximate check of the engine parameters saying 2,4,6 and 3 Representing N1 / EGT / N2 / FF are 20% / 400°C / 60% / 300kg/hr
On the NEO, the Basic check of idle parameters is slightly different. The middle two figures have increase by one so it's 2,5,7 and 3 representing N1 / EGT / N2 / FF are 20% / 500°C / 70% / 300kg/hr

The biggest difference with the start is a new function performed by FADEC called pre-start motoring or dry cranking. Depending on the thermal state of the engine, FADEC will dry crank for up to 60 seconds prior to initiation of the start sequence. This can happen on both automatic and manual starts. During this motoring, FADEC will limit the N2 to a maximum of about 30%.
Just for some additional, geeky, background information the reason for this is because After shutting down, the engine components cool at different rates because of natural convection, and this leads to varying thermal gradients across the shaft section of the engine which can cause vibration. So this cranking protects the engine, Airbus' term is Bow Rotor Protection by spinning the engine up getting airflow through it and makes the heat dissipate evenly throughout the hot section components prior to engine start.

Airbus have also changed some of the terminology around the engines idle states.
IDLE
What was 'modulated idle' on the CEO is now called ‘Minimum Idle’ on the NEO.
Approach Idle, which is a higher thrust setting than Minimum Idle to allow the engines to accelerate from Idle to TOGA thrust in the required regulatory time is now set when landing flap is selected (CONF 3 or FULL) or if the gear is selected down. For the CEO, Approach Idle is set when the flap lever is not in the zero position, basically with selection of Flap 1.

Max oil quantity is increased from 22QTS to 24.25QTS.
Minimum QTY increased from 9.5qt + 0.5qt/hour to 10.6qt + 0.45qt/hour.
Minimum oil temperature for start increased from -40°C to -29°C
Minimum oil temperature for take-off increased from -10°C to +19°C, so quite a difference there.

Starter limits are now as follows,
Starter:
Maximum number of start attempts reduced from four to three.
Pause between start attempts increased from 20s to 60s
Maximum running engagement of starter increased from 20% N2 to 59% N2

The EGT limits have changed and the amber and red bands reflect this. The operation is the same so we're not going to read off all these figures and they'll just get lost in our minds.

N1 Max has been reduced from 104% to 101% and N2 MAX has increased from 105% to 116.5%

The vibration displays have changed giving three options now, green, pulsing green and amber. The amber indication isn't available on the CEO. This also come with a new ECAM alert which triggers when the high vibration threshold is reached on N1 or N2. Crew are then directed to action the High Engine Vibration Checklist. The ECAM will say,
HI ENG VIB PROC...................................................................................................APPLY
Of course on the CEO you just get the advisory pulsing.

Next, wind limitations, yep, they've changed those too!
Wind limitation for starting: Max crosswind 45kts.
The crosswinds are different for take off and landing like they used to be with A max of 35kts for T.OFF and 38kts for Landing.
For automatic landing and roll-out:
Max Headwind 20kts
Max Tailwind 5kts
- Max Crosswind 15kts

Turbulence Penetration Speeds have been increased from 250kts to 260kts (below FL200) and from 275kts to 280kts (above FL200).

An Engine run-up is only required on the NEO if icing conditions exceed 60mins (it is 30mins on the CEO). After the 60 minutes, the engines should be increased to 70% for at least 5 seconds.
When operating in ground fog icing conditions, an engineering inspection should be performed on the engine if take-off not performed with 120mins

Something that's worth mentioning for those of you operating outside of Europe, the NEO has a restriction in the landing flap at high altitude airports. If the airport pressure altitude >2000ft, you have to use Flap 3 for approach if a minimum go around gradient of 4% can't be achieved. Theres a table in the FCOM-LIM section where you can check the restricting weight - most are well above MLW. This flap restriction will only occur below MLW at very high temperatures or very high pressure altitudes).

Probably the most noticeable difference for the crew is the automatic anti icing system. Within the engine, the NEO will automatically introduce hot air to the engine core when required to prevent ice crystal formation in the CORE of the engine, 'CORE ICE PROT’ is displayed on the ENG SD when it's active. It Also has a Booster Anti-Ice for prevention of ice in the booster section of the engine (‘BOOST ICE PROT’ is indicated on ENG SD Page when it's active. Remember though, these new features are only for internal anti-icing and don't remove the requirements for us to use engine anti ice

Another feature that's been added is protection against uncontrolled high thrust during critical phases of flight. This is called Thrust Control Malfunction Accommodation (TCMA) and is active on the ground and during takeoff and the approach phase. The TCMA protection logic will reduce fuel flow in flight or shutoff fuel on the ground, whenever an over-thrust condition is detected.
There's also something called a Transient Bleed Valve (TBV) which reduces the risk of engine stall during acceleration or deceleration of the engine.

There are some new memos which appear on the E/WD which are only available when the thrust levers are in TOGA or FLX/MCT detent. They are all displaying in a line above the N1 gauges.
With PACK pb-sw selected ON, 'PACKS' (MEMO)
When WAI is selected ON, 'WAI' (MEMO)
When EAI is selected ON, 'NAI' (MEMO)

FADEC has some new features too.
Transmission of vibration information to cockpit indicators
Protection against engine stall and engine flame-out
Thrust Control Malfunction Accommodation
Protection against bowed rotor during engine start on ground
Terminology difference: The CEO FADEC is also referred to as the ECU (Engine Control
Unit). The NEO FADEC is referred to as the EEC (Electronic Engine Control).

This week we take a more detailed look at an AC BUS 1 FAULT, firstly having a quick review of the system, the ECAM procedure and status page, and finally a discussion on how to handle it and some of the pitfalls! 

This week we're discussing the exciting topic of the A320 doors. Not the most inspiring subject but we'll make it nice an easy to digest for you today and hopefully make it interesting.

As usual with our systems episodes, we will go through the main points, then look at each type of door in more detail and then look at the controls and indicators for them all.

This week we are going continue our series of non technical discussions and  take a look at the role of pilot monitoring and its importance. This podcast isn't exclusive to the A320 and  the principals we will be discussing can be applied to all multi crew environments. 

We will cover what monitoring actual is, how we do it, what happens when monitoring is impaired and finally, how we can improve our own monitoring. 

This week we are looking at an air crash investigation. It's a follow-on from the CRM episode we did a couple of weeks ago.  If you haven't listened to that one then it may be worth a listen because we discussed situational Awareness.

Here are the links to the reports discussed

Kegworth - https://www.gov.uk/aaib-reports/4-1990-boeing-737-400-g-obme-8-january-1989

TransAsia Accident - https://www.asc.gov.tw/main_en/docaccident.aspx?uid=343&pid=296&acd_no=191

This system supplies high pressure air for air conditioning, engine starting, wing anti - icing, water pressurisation and hydraulic reservoir pressurisation. There are quite a few differences between the CEO and NEO aircraft so we will try and cover them in this episode. 

There are 3 high pressure sources: Engine bleed systems, APU load compressor and the HP ground connection. A crossbleed duct interconnects the engine bleed systems and receives air from the APU and ground sources when required. There is a valve mounted in this duct which allows the left and right side of the system to be interconnected. 

The system is controlled by 2 bleed management computers, BMC1 and BMC2. 

A leak detection system detects any overheating in the hot air ducts. 

Scenario of the week - You get an ECAM caution AIR L WING LEAK. What actions will you have to take? can you continue to destination or do you need to divert? Have a think about it, consult the FCOM and let us know your thoughts on our Facebook page or via twitter. 

Situational Awareness

"The perception of the elements in the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future" Mica Endsley 1988

3 levels (or stages) -

- Perception
- Comprehension
- Projection

4 Categories of SA -

Geographical

Spatial/Temporal

Systems

Environmental

Types of stress

Physical - noise, vibration, heat, cold and fatigue,
Psychological - mental load, time pressure, perceived time pressure, consequences of events fear, anxiety, uncertainty.

High workload is a form of stress and can be either long term high workload like a 4 sector day in busy airspace, with an inexperienced crew, or short term or even momentary high workload or overload like bad weather on approach.

These “clues” can warn of an error chain in progress – a series of events that may lead to an accident. Most accidents involving human error include at least four of these clues. They have been taken from an article written by Douglas Schwartz for FlightSafety International.

-Ambiguity - Information from two or more sources that doesn’t agree.

-Fixation- Focusing on any one thing to the exclusion of everything else.

-Confusion- uncertainty or bafflement about a situation (often accompanied by -anxiety or psychological discomfort).

-Failure to fly the aircraft - Everyone is focused on non-flying activities. (remember the infamous tristar crew that crashed into the everglades because all three of them were fixated on a blown bulb?)

-Failure to look outside… everyone heads down.

-Failure to meet expected checkpoint on flight plan or profile ETA, fuel burn, etc.

-Failure to adhere to SOPs.

-Failure to comply with limitations, minimums, regulatory requirements, etc.

-Failure to resolve discrepancies – contradictory data or personal conflicts.

-Failure to communicate fully and effectively – vague or incomplete statements.

How can improve our situational awareness.

These 10 tips were also part of Douglas Schwartz's article.

1 - Predetermine crew roles for high-workload phases of flight
2 - Develop a plan and assign responsibilities for handling problems and distractions
3 - Encourage input from all crew members, including cabin, ATC, maintenance, dispatch, etc
4 - Rotate your attention from the aircraft to flight path to crew – don’t fixate on one thing
5 - Monitor and evaluate your current status compared to your plan
6 - Project ahead and consider contingencies (for example if you hear aircraft ahead being told to hold)
7 - Focus on the details and scan the big picture
8 - Create visual and/or aural reminders of interrupted tasks (this could be as simple as keeping your finger on a checklist line)
9 - Watch for clues of degraded SA
10 - Speak up when you see SA breaking down

Links

http://www.pacdeff.com/pdfs/AviationSA-Endsley%201999.pdf

In this weeks episode we cover the last few items of our abnormal electrical system. These are AC ESS BUS FAULT, DC ESS BUSS FAULT, DC 1 and 2 BUS FAULT and the EMERGENCY ELECTRICAL CONFIG.

All the ECAM items can be found in the FCOM.

For the scenario of the week we want you to have a look at the Emer Elec Config pages in the QRH and think about how you will deal with it and what considerations you have to make before attempting an approach.

Listen to Matt and Andy repeatedly say LGCIU for 15 minutes!

The main components are two main landing gear with two wheels on each that retract inboard and one nose wheel gear with two wheels that retracts forwards.

The landing gear and the doors are electrically controlled and hydraulically operated.

Landing Gear Control Interface units form a significant part of the A320. Because they are in charge sending landing gear position data to other aircraft systems, loss of both can have far reaching consequences.

LGCIUs receive all this data from three sets of proximity sensors. The ones for the landing gear, the ones for the cargo doors and the ones for the flaps.
So, for the landing gear, they receive information about when....
- The landing gears are locked down or up, or
- The shock absorbers are compressed or extended, or
- The landing gear doors are open, or closed, or
- The bogie are aligned or not.

From the cargo doors, they receive the position of the following components :
The Manuel selector valves
The Locking shaft
The Locking handle
and Safety shaft

The LGCIUs detect electrical failures only those last three proximity switches,
The Locking shaft,
The Locking handle,
and the Safety shaft.
If an LGCIU detects one of these failures, it indicates the NON LOCKED condition for that component.

Finally, the LANDING FLAPS INFORMATION.
The LGCIUs receives the signals from four flap disconnect proximity switches,and then sends them on to the Slat/Flap Control Computers (SFCCs). The LGCIUs do not monitor failures in the SFCC system though.

Gravity Gear extension actions

GRAVITY GEAR EXTN .......................................... PULL AND TURN
L/G lever...................................................................... DOWN
GEAR DOWN indications (if available)...................... CHECK

The biggest lesson to take away from this is, read all the checklist before you make an approach so you can go through all the notes, then leave the QRH open on this page ready for the approach so when PF calls for gear down, only the three items can be read and done.

max speed with landing gear extended...........280 kts
max speed to extend the gear..........................250 kts
max speed to retract the gear..........................220 kts

Above 260 kts a safety valve automatically cuts off hydraulic supply.

Scenario of the week

Think about what you would do if you had a 'gear not downlocked' and the gravity extension didnt work. Have a look at the QRH and come up with a plan of how you will organise and manage the situation. There's a lot to consider here and many of the decisions you make could have critical consequences. Comment on our facebook page at facebook.com/A320podcast or tweet us using @A320Podcast.

Generator Failure

If one engine generator fails, the system will automatically replace the failed generator with the APU generator, if it is available, or the other engine generator. Part of the galley load will be shed automatically and, if fitted, the DC entertainment bus will also be shed. 

So if an engine generator is lost the entire system can be supplied by the remaining engine generator or the APU so the entire system remains powered.

Failure of AC Bus

If AC BUS 1 fails AC BUS 2 can supply the AC ESS BUS and the ESS TR can supply  the DC ESS BUS.  Depending on the MSN of the aircraft this either occurs automatically or can be recovered by switching the AC ESS FEED to ALTN on the overhead panel. If manual switching is required both the AC and DC ESS BUS FAULTS will show on the ECAM. DC BUS 2 supplies DC BUS 1 and DC BAT BUS automatically after 5 seconds. 

TR failure

TR1 or TR2 can supply both DC BUS1 and DC BUS2 via the DC BAT BUS. so if TR 2 fails to slack is taken up by TR1 and DC BUS 2 is supplied via the DC BAT BUS and vice versa.

A TR 1 or 2 FAULT ECAM caution is for crew awareness. The status page states the aircraft is now cat 3 single and the inop systems are the associated TR and cat 3 dual. 

If TR1 fails the DC ESS BUS looses its power source so in this case the ESS TR via the AC ESS bus, will power the DC ESS bus. 

Failure of a DC BUS

DC BUS 1 Fault 

The system display will show DC 1 in amber and, as with a TR 1 fault the DC ESS BUS is now powered via the ESS TR. 

DC BUS 2 FAULT

AIR DATA SWTG - F/O 3. as the First officers side has lost air data this is self explanatory. 

BARO REF CHECK - SINCE FCU CHANNEL 2  is lost the barometer settings need to be crosschecked on the FCU and PFD. 

Secondary systems

CAB PRESS - SYS 2 in amber

FUEL - L+R tank and Centre tank pump 2 inop

WHEEL - gear indications missing due to LGCIU 1 + 2 in op

F/CTL - SPOILERS 1 2 AND 5 INOP ELAC 2 AND  SEC 2 AND 3 IN OP

Read ECAM source:

https://www.facebook.com/A320-IPAD-ECAM-1849879165252506/

There are three types of aquaplaning - viscous, rubber reversion, and dynamic.

Viscous

This occurs when a thin film of contaminant creates a break in the contact of the tyre with the runway surface. This type normally only occurs on unusually smooth surfaces such as the runway touchdown zone where there is an excessive build-up of rubber. Viscous aquaplaning can occur even in damp conditions at high and low speeds. Because there's no actual contact, no marks are left on the runway.

Reverted rubber

This type of aquaplaning occurs when a stationary tyre (so either 'locked up' during braking or at touchdown) is dragged across a surface causing friction at the contact point. The heat produced by the friction boils the water on the surface creating steam. The pressure of the steam lifts the centre of the tyre off the surface leaving the edges still in contact creating a seal which traps the steam, this then melts the rubber and reverts it to its unvulcanised state. Friction levels during this type of aquaplaning are the equivalent of icy runways. The tyre will have 'bubbled' rubber deposits on it and the runway will show marks in the form of being pressure washed as the tyre effectively 'steam cleaned' it.

Dynamic aquaplaning

Now this is the most common type of aquaplaning and the one that's most likely to affect us. Aircraft in general are prone to this one because it's a relatively high-speed phenomenon that occurs when there is a film of water on the runway that is at least 2.5 mm deep. As the speed of the aircraft and the depth of the water increase, the water layer builds up an increasing resistance to displacement, resulting in the formation that wall of water beneath the tire we mentioned earlier. Once the tyre speed gets to the point where it can no longer displace the water quick enough it starts to aquaplane. At some speed, termed the aquaplaning speed (Vp), the upward force generated by water pressure equals the weight of the aircraft and the tire is lifted off the runway surface. In this condition, the tires no longer contribute to directional control, and braking action becomes very poor once in this state. 
When we use the landing distance calculations, aquaplaning is taken into account when contaminated performance is selected. Airbus says "Performance data for landing on runways contaminated with standing water, slush and snow include accountability for the reduced wheel braking on the contaminated runway including negligible wheel braking above the hydroplaning speed." 
As there is no surface contact during dynamic aquaplaning, there are no marks left on the runway surface or the tyre.

The minimum speed for dynamic aquaplaning (Vp) in knots is about 9 times the square root of the tire pressure in pounds per square inch (PSI). The pressures on our airbus' vary depending on the MSN number but there is a placard on the back of each main undercarriage strut with the required pressure. As an example though, if an A319 has a pressure of 200 PSI, then the aquaplaning speed would be 127kts, surprisingly similar to the sort of speeds we touchdown at! A locked up wheel will aquaplane at much lower speeds - as low as 7.7√P which would be only 108kts! And once aquaplaning has started it can continue at speeds well below this.

If you touch down with some crab angle on a dry runway, the aircraft automatically realigns with the direction of travel down the runway.

But on a contaminated runway, the aircraft tends to travel along the runway centerline with the existing crab angle. This is then compounded by the side force created by the crosswind component on the fuselage and the tail fin which tends to make the aircraft skid sideways (downwind) off the centerline.

If full reverse is applied as is recommended, you could end up in a situation where you're skidding down the runway at an angle and no amount of rudder will straighten you up. This is because the reverse thrust results into two force components, a stopping force aligned along the aircraft direction of travel (runway centerline), and a side force, perpendicular to the runway centerline, which further increases the tendency to skid sideways. As the airspeed decreases, the rudder efficiency decreases and is also made worse by the airflow disruption created by the engine reverse airflow.

To get out if this situation it's quite counterintuitive. The harder the wheel braking force, the lower the tire-cornering force, so if the aircraft tends to continue skidding sideways. Releasing the brakes (by taking over from the autobrake) increases the tire-cornering force and helps to maintain or regain directional control.

Selecting reverse idle cancels the effects of reverse thrust (the side force and rudder airflow disruption) and helps in regaining directional control.

Once directional control has been recovered and the runway centerline has been regained:

• Pedal braking can be applied as required, and

• Reverse thrust can be reselected.

In conclusion then, if it is thought that there is a possibility of aquaplaning, then a positive touchdown should be made using MED autobrake and full reversers. It should also be remembered that if aquaplaning starts to occur, braking coefficient will be the equivalent of an icy runway. If unsure, as mentioned before, the landing performance calculations can be selected to a contaminated state to take aquaplaning into account.

If a crabbing skid is experienced after touchdown and directional control is lost,
cancel reverse and release brakes
Regain directional control and the centerline
Reverse thrust and pedal braking can then be reapplied