Australian Aviation — January 2018

Volcanic ash

Passengers seem more patient

with volcano-induced flight

interruptions.AAP IMAGE

Volcanic ash covers a

Boeing 737 at Solo, central Java,

Indonesia in February 2014.

AAP IMAGE

allow the aircraft to exit the ash cloud.
Climbing above it may not be possible
and even if it was, the increase in
thrust would actually increase the
engine temperature and in turn,
increase the melting debris bonding
to the engine, making the situation
worse.
For this reason, a reduction in
thrust to idle may lessen the build-
up of molten material, although it
will also make the 180-degree turn a
descending turn, so terrain must be
considered. In autothrottle-equipped
aircraft, it may be worth considering
disconnecting the autothrottle to
avoid the thrust increasing unnoticed.
Notably, with the engines at idle,
as opposed to flamed out, electrical
power, bleed air, hydraulics and
pressurisation all remain available. If
possible, starting the auxiliary power
Unit (APU) may be able to provide an
alternate source of electrical power
and/or bleed air for engine starting on
certain aircraft types.
On the flightdeck the crew should
don their oxygen masks and goggles to
counter the fumes and haze. Turning
on engine and wing anti-ice devices
and all air-conditioning packs may
also increase the engines’ stall margins

by increasing airflow, while selection

of continuous ignition will be of

benefit if a restart is needed.

Should the unthinkable occur and

multiple engines flame out, cycling

the fuel switches/start levers to ‘off’

and then ‘on’ in an attempt to restart

the engines is a procedure common to

many aircraft types. The engines may

be very slow to spool up, so they need

to be monitored closely and patiently

and guarded against rapidly rising

exhaust gas temperatures (EGT).

This would be a very bad day for

any airline crew, but it is of some

reassurance that pilots are trained

in the specific procedures relating to

their specific aircraft in this situation.

And like all emergencies, it is always

best to be thoroughly prepared.

Ash clouds rising

While aircraft are still vulnerable to

volcanic ash and without a system

of onboard detection, pilots and

passengers are in a totally different

situation to when Speedbird 9 had

its ash cloud encounter more than

thirty years ago. International bodies,

airlines and pilots are far better

informed, educated and trained in this

threatening phenomenon. A wealth

of information is continually gathered

and shared around the world and

airlines and pilots alike opt for the

conservative option.

This approach may lead to

cancelled flights and the disruption

of family plans, but the extensive

queues in airline terminals are truly

a small price to pay. The commercial

impact upon airlines is also great,

but their crew and passengers’

welfare must always be the overriding

consideration. In aviation, safety must

always be the priority and there is

nothing to be gained by challenging

Mother Nature when the ash clouds

are rising.